If this problem hasn't already been reported, please open a ticket
at https://github.com/dmulloy2/ProtocolLib/issues with the following data:
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:458)
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$spin$0(MinecraftServer.java:311)
at java.base/java.lang.Thread.run(Thread.java:1583)
Dump:
Parameters:
[NULL]
Sender:
com.comphenix.protocol.ProtocolLib@61d55101[
statistics=
packetTask=
tickCounter=0
configExpectedMod=-1
updater=com.comphenix.protocol.updater.SpigotUpdater@65db3ba1
redirectHandler=
scheduler=com.comphenix.protocol.scheduler.DefaultScheduler@2ecd3342
commandProtocol=
commandPacket=
commandFilter=
packetLogging=
skipDisable=false
isEnabled=false
loader=org.bukkit.plugin.java.JavaPluginLoader@29a895e2
server=CraftServer{serverName=CraftBukkit,serverVersion=4195-Spigot-fcd94e2-f057cf4,minecraftVersion=1.20.6}
file=plugins/ProtocolLib (1).jar
description=org.bukkit.plugin.PluginDescriptionFile@44a472c2
dataFolder=plugins/ProtocolLib
classLoader=org.bukkit.plugin.java.PluginClassLoader@1abc27f2
naggable=true
newConfig=YamlConfiguration[path='', root='YamlConfiguration']
configFile=plugins/ProtocolLib/config.yml
logger=org.bukkit.plugin.PluginLogger@2e5be8a2
]
Version:
ProtocolLib v5.1.0
Java Version:
21.0.3
Server:
4195-Spigot-fcd94e2-f057cf4 (MC: 1.20.6)

Should be fixed in the latest dev build so please use the latest dev build and try again: https://ci.dmulloy2.net/job/ProtocolLib/lastSuccessfulBuild/