---- Minecraft Crash Report ----
// I bet Cylons wouldn't have this problem.

Time: 2025-01-25 08:30:11
Description: Exception in server tick loop

java.lang.NoSuchMethodError: 'net.minecraft.class_2168 net.minecraft.class_3222.method_64396()'
at knot//me.lucko.fabric.api.permissions.v0.Util.commandSourceFromEntity(Util.java:38)
at knot//me.lucko.fabric.api.permissions.v0.Permissions.check(Permissions.java:174)
at knot//eu.pb4.polymer.common.impl.CommonImplUtils.permissionCheck(CommonImplUtils.java:112)
at knot//eu.pb4.polymer.core.api.item.PolymerItemGroupUtils.getContentsFor(PolymerItemGroupUtils.java:39)
at knot//eu.pb4.polymer.core.impl.networking.payloads.s2c.PolymerItemGroupContentAddS2CPayload.of(PolymerItemGroupContentAddS2CPayload.java:30)
at knot//eu.pb4.polymer.core.impl.networking.PolymerServerProtocol.syncItemGroupContents(PolymerServerProtocol.java:213)
at knot//eu.pb4.polymer.core.impl.networking.PolymerServerProtocol.syncItemGroup(PolymerServerProtocol.java:199)
at knot//eu.pb4.polymer.core.impl.networking.PolymerServerProtocol.sendCreativeSyncPackets(PolymerServerProtocol.java:186)
at knot//eu.pb4.polymer.core.impl.networking.PolymerServerProtocol.sendSyncPackets(PolymerServerProtocol.java:126)
at knot//eu.pb4.polymer.core.impl.networking.PolymerServerProtocolHandler.lambda$register$0(PolymerServerProtocolHandler.java:36)
at knot//net.minecraft.class_3324.md0de984$polymer-networking$lambda$polymerNet$setupHandler$0$0(class_3324.java:3999)
at knot//eu.pb4.polymer.common.api.events.SimpleEvent.invoke(SimpleEvent.java:28)
at knot//net.minecraft.class_3324.handler$bgm000$polymer-networking$polymerNet$setupHandler(class_3324.java:3999)
at knot//net.minecraft.class_3324.method_14570(class_3324.java:202)
at knot//net.minecraft.class_8610.mixinextras$bridge$method_14570$32(class_8610.java)
at knot//net.minecraft.class_8610.wrapOperation$bgo000$polymer-networking$polymerNet$prePlayHandshakeHackfest(class_8610.java:1038)
at knot//net.minecraft.class_8610.method_52408(class_8610.java:152)
at knot//net.minecraft.class_8736.method_53043(class_8736.java:22)
at knot//net.minecraft.class_8736.method_11054(class_8736.java:8)
at knot//net.minecraft.class_2600.method_11072(class_2600.java:27)
at knot//net.minecraft.class_3738.run(class_3738.java:18)
at knot//net.minecraft.class_1255.method_18859(class_1255.java:162)
at knot//net.minecraft.class_4093.method_18859(class_4093.java:23)
at knot//net.minecraft.server.MinecraftServer.method_24306(MinecraftServer.java:864)
at knot//net.minecraft.server.MinecraftServer.method_18859(MinecraftServer.java:173)
at knot//net.minecraft.class_1255.method_16075(class_1255.java:136)
at knot//net.minecraft.server.MinecraftServer.method_20415(MinecraftServer.java:846)
at knot//net.minecraft.server.MinecraftServer.method_16075(MinecraftServer.java:840)
at knot//net.minecraft.class_1255.method_18857(class_1255.java:145)
at knot//net.minecraft.server.MinecraftServer.method_18857(MinecraftServer.java:810)
at knot//net.minecraft.server.MinecraftServer.method_16208(MinecraftServer.java:815)
at knot//net.minecraft.server.MinecraftServer.method_29741(MinecraftServer.java:702)
at knot//net.minecraft.server.MinecraftServer.method_29739(MinecraftServer.java:281)
at java.base/java.lang.Thread.run(Thread.java:1583)

A detailed walkthrough of the error, its code path and all known details is as follows:

-- Cobblemon --
Details:
Version: 1.6.0
Is Snapshot: false
Git Commit: 2e3302b (https://gitlab.com/cable-mc/cobblemon/-/commit/2e3302bdec487bf11cace370cffd38f1837ae96b)
Branch: HEAD

-- System Details --
Details:
Minecraft Version: 1.21.1
Minecraft Version ID: 1.21.1
Operating System: Windows 11 (amd64) version 10.0
Java Version: 21.0.3, Microsoft
Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Microsoft
Memory: 920334512 bytes (877 MiB) / 2600468480 bytes (2480 MiB) up to 4261412864 bytes (4064 MiB)
CPUs: 8
Processor Vendor: GenuineIntel
Processor Name: Intel(R) Core(TM) i3-10100F CPU @ 3.60GHz
Identifier: Intel64 Family 6 Model 165 Stepping 3
Microarchitecture: Comet Lake
Frequency (GHz): 3.60
Number of physical packages: 1
Number of physical CPUs: 4
Number of logical CPUs: 8
Graphics card #0 name: NVIDIA GeForce 210
Graphics card #0 vendor: NVIDIA
Graphics card #0 VRAM (MiB): 1024.00
Graphics card #0 deviceId: VideoController1
Graphics card #0 versionInfo: 21.21.13.4201
Memory slot #0 capacity (MiB): 8192.00
Memory slot #0 clockSpeed (GHz): 2.67
Memory slot #0 type: Unknown
Virtual memory max (MiB): 17318.01
Virtual memory used (MiB): 12818.19
Swap memory total (MiB): 9216.00
Swap memory used (MiB): 828.52
Space in storage for jna.tmpdir (MiB): available: 1759.87, total: 227038.00
Space in storage for org.lwjgl.system.SharedLibraryExtractPath (MiB): available: 1759.87, total: 227038.00
Space in storage for io.netty.native.workdir (MiB): available: 1759.87, total: 227038.00
Space in storage for java.io.tmpdir (MiB): available: 1759.87, total: 227038.00
Space in storage for workdir (MiB): available: 1759.87, total: 227038.00
JVM Flags: 8 total; -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=16M -Xmx4051m -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump
Fabric Mods:
cobblemon: Cobblemon 1.6.0+1.21.1
fabric-language-kotlin: Fabric Language Kotlin 1.11.0+kotlin.2.0.0
org_jetbrains_kotlin_kotlin-reflect: kotlin-reflect 2.0.0
org_jetbrains_kotlin_kotlin-stdlib: kotlin-stdlib 2.0.0
org_jetbrains_kotlin_kotlin-stdlib-jdk7: kotlin-stdlib-jdk7 2.0.0
org_jetbrains_kotlin_kotlin-stdlib-jdk8: kotlin-stdlib-jdk8 2.0.0
org_jetbrains_kotlinx_atomicfu-jvm: atomicfu-jvm 0.24.0
org_jetbrains_kotlinx_kotlinx-coroutines-core-jvm: kotlinx-coroutines-core-jvm 1.8.1
org_jetbrains_kotlinx_kotlinx-coroutines-jdk8: kotlinx-coroutines-jdk8 1.8.1
org_jetbrains_kotlinx_kotlinx-datetime-jvm: kotlinx-datetime-jvm 0.6.0
org_jetbrains_kotlinx_kotlinx-serialization-cbor-jvm: kotlinx-serialization-cbor-jvm 1.6.3
org_jetbrains_kotlinx_kotlinx-serialization-core-jvm: kotlinx-serialization-core-jvm 1.6.3
org_jetbrains_kotlinx_kotlinx-serialization-json-jvm: kotlinx-serialization-json-jvm 1.6.3
fabric-api: Fabric API 0.115.0+1.21.1
fabric-api-base: Fabric API Base 0.4.42+6573ed8c19
fabric-api-lookup-api-v1: Fabric API Lookup API (v1) 1.6.70+b559734419
fabric-biome-api-v1: Fabric Biome API (v1) 13.0.31+d527f9fd19
fabric-block-api-v1: Fabric Block API (v1) 1.0.22+0af3f5a719
fabric-block-view-api-v2: Fabric BlockView API (v2) 1.0.10+6573ed8c19
fabric-blockrenderlayer-v1: Fabric BlockRenderLayer Registration (v1) 1.1.52+0af3f5a719
fabric-client-tags-api-v1: Fabric Client Tags 1.1.15+6573ed8c19
fabric-command-api-v1: Fabric Command API (v1) 1.2.49+f71b366f19
fabric-command-api-v2: Fabric Command API (v2) 2.2.28+6ced4dd919
fabric-commands-v0: Fabric Commands (v0) 0.2.66+df3654b319
fabric-content-registries-v0: Fabric Content Registries (v0) 8.0.18+b559734419
fabric-convention-tags-v1: Fabric Convention Tags 2.1.2+7f945d5b19
fabric-convention-tags-v2: Fabric Convention Tags (v2) 2.9.2+e60e56d419
fabric-crash-report-info-v1: Fabric Crash Report Info (v1) 0.2.29+0af3f5a719
fabric-data-attachment-api-v1: Fabric Data Attachment API (v1) 1.4.1+9ed317f519
fabric-data-generation-api-v1: Fabric Data Generation API (v1) 20.2.25+16c4ae2519
fabric-dimensions-v1: Fabric Dimensions API (v1) 4.0.0+6fc22b9919
fabric-entity-events-v1: Fabric Entity Events (v1) 1.7.0+2122d82819
fabric-events-interaction-v0: Fabric Events Interaction (v0) 0.7.13+ba9dae0619
fabric-game-rule-api-v1: Fabric Game Rule API (v1) 1.0.53+6ced4dd919
fabric-item-api-v1: Fabric Item API (v1) 11.1.1+d5debaed19
fabric-item-group-api-v1: Fabric Item Group API (v1) 4.1.6+6823f7cd19
fabric-key-binding-api-v1: Fabric Key Binding API (v1) 1.0.47+0af3f5a719
fabric-keybindings-v0: Fabric Key Bindings (v0) 0.2.45+df3654b319
fabric-lifecycle-events-v1: Fabric Lifecycle Events (v1) 2.5.0+01d9a51c19
fabric-loot-api-v2: Fabric Loot API (v2) 3.0.15+3f89f5a519
fabric-loot-api-v3: Fabric Loot API (v3) 1.0.3+3f89f5a519
fabric-message-api-v1: Fabric Message API (v1) 6.0.13+6573ed8c19
fabric-model-loading-api-v1: Fabric Model Loading API (v1) 2.0.0+fe474d6b19
fabric-networking-api-v1: Fabric Networking API (v1) 4.3.0+c7469b2119
fabric-object-builder-api-v1: Fabric Object Builder API (v1) 15.2.1+40875a9319
fabric-particles-v1: Fabric Particles (v1) 4.0.2+6573ed8c19
fabric-recipe-api-v1: Fabric Recipe API (v1) 5.0.14+248df81c19
fabric-registry-sync-v0: Fabric Registry Sync (v0) 5.2.0+34f5d91419
fabric-renderer-api-v1: Fabric Renderer API (v1) 3.4.0+c705a49c19
fabric-renderer-indigo: Fabric Renderer - Indigo 1.7.0+c705a49c19
fabric-renderer-registries-v1: Fabric Renderer Registries (v1) 3.2.68+df3654b319
fabric-rendering-data-attachment-v1: Fabric Rendering Data Attachment (v1) 0.3.48+73761d2e19
fabric-rendering-fluids-v1: Fabric Rendering Fluids (v1) 3.1.6+1daea21519
fabric-rendering-v0: Fabric Rendering (v0) 1.1.71+df3654b319
fabric-rendering-v1: Fabric Rendering (v1) 5.0.5+df16efd019
fabric-resource-conditions-api-v1: Fabric Resource Conditions API (v1) 4.3.0+8dc279b119
fabric-resource-loader-v0: Fabric Resource Loader (v0) 1.3.1+5b5275af19
fabric-screen-api-v1: Fabric Screen API (v1) 2.0.25+8b68f1c719
fabric-screen-handler-api-v1: Fabric Screen Handler API (v1) 1.3.88+b559734419
fabric-sound-api-v1: Fabric Sound API (v1) 1.0.23+6573ed8c19
fabric-transfer-api-v1: Fabric Transfer API (v1) 5.4.2+c24bd99419
fabric-transitive-access-wideners-v1: Fabric Transitive Access Wideners (v1) 6.2.0+45b9699719
fabric-permissions-api-v0: fabric-permissions-api 0.3.3
fabricloader: Fabric Loader 0.16.10
mixinextras: MixinExtras 0.4.1
flourish: Flourish 1.4.2
adventure-platform-fabric: adventure-platform-fabric 5.14.1
net_kyori_adventure-api: adventure-api 4.17.0
net_kyori_adventure-key: adventure-key 4.17.0
net_kyori_adventure-platform-api: adventure-platform-api 4.3.3
net_kyori_adventure-text-logger-slf4j: adventure-text-logger-slf4j 4.17.0
net_kyori_adventure-text-minimessage: adventure-text-minimessage 4.17.0
net_kyori_adventure-text-serializer-ansi: adventure-text-serializer-ansi 4.17.0
net_kyori_adventure-text-serializer-gson: adventure-text-serializer-gson 4.17.0
net_kyori_adventure-text-serializer-json: adventure-text-serializer-json 4.17.0
net_kyori_adventure-text-serializer-plain: adventure-text-serializer-plain 4.17.0
net_kyori_ansi: ansi 1.1.0
net_kyori_examination-api: examination-api 1.3.0
net_kyori_examination-string: examination-string 1.3.0
net_kyori_option: option 1.0.0
stimuli: Stimuli 0.4.12+1.21
java: OpenJDK 64-Bit Server VM 21
minecraft: Minecraft 1.21.1
polymer-bundled: Polymer 0.9.18+1.21.1
polymer-blocks: Polymer (Textured Blocks) 0.9.18+1.21.1
polymer-common: Polymer (Common) 0.9.18+1.21.1
packet_tweaker: Packet Tweaker 0.5.5+1.21
polymer-core: Polymer (Core) 0.9.18+1.21.1
polymer-networking: Polymer (Networking) 0.9.18+1.21.1
polymer-registry-sync-manipulator: Polymer (Registry Sync Manipulator) 0.9.18+1.21.1
polymer-resource-pack: Polymer (Resource Pack) 0.9.18+1.21.1
polymer-virtual-entity: Polymer (Virtual Entity) 0.9.18+1.21.1
Server Running: true
Player Count: 0 / 8; []
Active Data Packs: vanilla, fabric, cobblemon, fabric-convention-tags-v2, flourish (incompatible), $polymer-resources, file/Souls Mega Pack-1.3 - 1.6.0.zip (incompatible)
Available Data Packs: $polymer-resources, bundle, cobblemon, fabric, fabric-convention-tags-v2, file/Souls Mega Pack-1.3 - 1.6.0.zip (incompatible), flourish (incompatible), trade_rebalance, vanilla
Enabled Feature Flags: minecraft:vanilla
World Generation: Stable
World Seed: 3393509522288487518
Type: Integrated Server (map_client.txt)
Is Modded: Definitely; Client brand changed to 'fabric'; Server brand changed to 'fabric'
Launched Version: fabric-loader-0.16.10-1.21.1

You have permission api version that isn't compatible with 1.21.1. Not polymer issue