Stack Trace:
java.lang.IllegalArgumentException: Unable to find a field that matches {modifiers=[required: 10000, banned: 1000], type={ type input instanceof interface java.util.Map }}
at com.comphenix.protocol.reflect.FuzzyReflection.getField(FuzzyReflection.java:352)
at com.comphenix.protocol.injector.packet.PacketRegistry.createNewRegister(PacketRegistry.java:168)
at com.comphenix.protocol.injector.packet.PacketRegistry.initialize(PacketRegistry.java:292)
at com.comphenix.protocol.injector.packet.PacketRegistry.getClientPacketTypes(PacketRegistry.java:327)
at com.comphenix.protocol.injector.PacketFilterManager.(PacketFilterManager.java:120)
at com.comphenix.protocol.injector.PacketFilterBuilder.build(PacketFilterBuilder.java:121)
at com.comphenix.protocol.ProtocolLib.onLoad(ProtocolLib.java:183)
at org.bukkit.craftbukkit.v1_20_R4.CraftServer.loadPlugins(CraftServer.java:435)
at net.minecraft.server.dedicated.DedicatedServer.e(DedicatedServer.java:232)
at net.minecraft.server.MinecraftServer.y(MinecraftServer.java:1010)
at net.minecraft.server.MinecraftServer.lambda$0(MinecraftServer.java:311)
at java.base/java.lang.Thread.run(Thread.java:1583)
Dump:
Parameters:
[NULL]
Sender:
com.comphenix.protocol.ProtocolLib@6f15c808[
statistics=
packetTask=
tickCounter=0
configExpectedMod=-1
updater=com.comphenix.protocol.updater.SpigotUpdater@40a240d4
redirectHandler=
scheduler=com.comphenix.protocol.scheduler.DefaultScheduler@1b68540
commandProtocol=
commandPacket=
commandFilter=
packetLogging=
skipDisable=false
isEnabled=false
loader=org.bukkit.plugin.java.JavaPluginLoader@7a48ca58
server=CraftServer{serverName=CraftBukkit,serverVersion=4109-Spigot-b698b49-8c1e7c8,minecraftVersion=1.20.5}
file=plugins/ProtocolLib.jar
description=org.bukkit.plugin.PluginDescriptionFile@1aea2a9f
dataFolder=plugins/ProtocolLib
classLoader=org.bukkit.plugin.java.PluginClassLoader@79c2669
naggable=true
newConfig=YamlConfiguration[path='', root='YamlConfiguration']
configFile=plugins/ProtocolLib/config.yml
logger=org.bukkit.plugin.PluginLogger@58864f71
]
Version:
ProtocolLib v5.1.0
Java Version:
21.0.2
Server:
4109-Spigot-b698b49-8c1e7c8 (MC: 1.20.5)

This is fixed in the latest dev builds. Find them here: https://ci.dmulloy2.net/job/ProtocolLib/