[09:54:38 WARN]: [ProtocolLib] Version (MC: 1.19.3) has not yet been tested! Proceed with caution.
[09:54:39 ERROR]: [ProtocolLib] INTERNAL ERROR: Cannot load ProtocolLib.
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.ExceptionInInitializerError
at ProtocolLib.jar//com.comphenix.protocol.injector.netty.ProtocolInjector.(ProtocolInjector.java:69)
at ProtocolLib.jar//com.comphenix.protocol.injector.PacketFilterManager.(PacketFilterManager.java:202)
at ProtocolLib.jar//com.comphenix.protocol.injector.PacketFilterBuilder.buildInternal(PacketFilterBuilder.java:185)
at ProtocolLib.jar//com.comphenix.protocol.injector.PacketFilterBuilder.build(PacketFilterBuilder.java:177)
at ProtocolLib.jar//com.comphenix.protocol.ProtocolLib.onLoad(ProtocolLib.java:203)
at io.papermc.paper.plugin.storage.ServerPluginProviderStorage.processProvided(ServerPluginProviderStorage.java:59)
at io.papermc.paper.plugin.storage.ServerPluginProviderStorage.processProvided(ServerPluginProviderStorage.java:18)
at io.papermc.paper.plugin.storage.SimpleProviderStorage.enter(SimpleProviderStorage.java:36)
at io.papermc.paper.plugin.entrypoint.LaunchEntryPointHandler.enter(LaunchEntryPointHandler.java:36)
at org.bukkit.craftbukkit.v1_19_R2.CraftServer.loadPlugins(CraftServer.java:428)
at net.minecraft.server.dedicated.DedicatedServer.e(DedicatedServer.java:273)
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:1101)
at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:316)
at java.base/java.lang.Thread.run(Thread.java:1589)
Caused by: java.lang.UnsupportedOperationException: Cannot define class using reflection: Unable to make protected java.lang.Package java.lang.ClassLoader.getPackage(java.lang.String) accessible: module java.base does not "opens java.lang" to unnamed module @34d1ccc1
at ProtocolLib.jar//com.comphenix.net.bytebuddy.dynamic.loading.ClassInjector$UsingReflection$Dispatcher$Initializable$Unavailable.defineClass(ClassInjector.java:471)
at ProtocolLib.jar//com.comphenix.net.bytebuddy.dynamic.loading.ClassInjector$UsingReflection.injectRaw(ClassInjector.java:283)
at ProtocolLib.jar//com.comphenix.net.bytebuddy.dynamic.loading.ClassInjector$AbstractBase.inject(ClassInjector.java:117)
at ProtocolLib.jar//com.comphenix.net.bytebuddy.dynamic.loading.ClassLoadingStrategy$Default$InjectionDispatcher.load(ClassLoadingStrategy.java:243)
at ProtocolLib.jar//com.comphenix.net.bytebuddy.dynamic.loading.ClassLoadingStrategy$Default.load(ClassLoadingStrategy.java:150)
at ProtocolLib.jar//com.comphenix.net.bytebuddy.dynamic.TypeResolutionStrategy$Passive.initialize(TypeResolutionStrategy.java:101)
at ProtocolLib.jar//com.comphenix.net.bytebuddy.dynamic.DynamicType$Default$Unloaded.load(DynamicType.java:6161)
at ProtocolLib.jar//com.comphenix.protocol.injector.server.TemporaryPlayerFactory.setupProxyPlayerConstructor(TemporaryPlayerFactory.java:187)
at ProtocolLib.jar//com.comphenix.protocol.injector.server.TemporaryPlayerFactory.(TemporaryPlayerFactory.java:51)
... 14 more
Dump:
Parameters:
[NULL]
Sender:
com.comphenix.protocol.ProtocolLib@794a26e8[
statistics=
backgroundCompiler=
packetTask=-1
tickCounter=0
unhookTask=com.comphenix.protocol.injector.DelayedSingleTask@6ab98868
configExpectedMod=-1
updater=com.comphenix.protocol.updater.SpigotUpdater@42ec9eb1
redirectHandler=
commandProtocol=
commandPacket=
commandFilter=
packetLogging=
skipDisable=false
isEnabled=false
loader=io.papermc.paper.plugin.manager.DummyBukkitPluginLoader@72fb70bb
server=CraftServer{serverName=Paper,serverVersion=git-Paper-445,minecraftVersion=1.19.3}
file=plugins\ProtocolLib.jar
description=org.bukkit.plugin.PluginDescriptionFile@2ce9eb5b
pluginMeta=org.bukkit.plugin.PluginDescriptionFile@2ce9eb5b
dataFolder=plugins\ProtocolLib
classLoader=PluginClassLoader{plugin=ProtocolLib v4.8.0, pluginEnabled=false, url=plugins\ProtocolLib.jar}
naggable=true
newConfig=YamlConfiguration[path='', root='YamlConfiguration']
configFile=plugins\ProtocolLib\config.yml
logger=com.destroystokyo.paper.utils.PaperPluginLogger@75545801
]
Version:
ProtocolLib v4.8.0
Java Version:
19.0.1
Server:
git-Paper-445 (MC: 1.19.3)

#2165 (comment)
and i'm not sure if Java 19 is supported yet...