The new generation system broke regen support in 1.21 by a large amount

Yeah it just errors for me completely.
Here the error if its helpfull, I feel this is more of a bug fix instead of a Enhancement

[10:53:50] [AsyncNotifyKeyedQueue - 0/ERROR]: An unexpected error while handling a FastAsyncWorldEdit command
java.lang.IllegalAccessError: class com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_21_R1.regen.PaperweightRegen tried to access private field net.minecraft.server.level.PlayerChunkMap.P (com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_21_R1.regen.PaperweightRegen is in unnamed module of loader org.bukkit.plugin.java.PluginClassLoader @52f7d97b; net.minecraft.server.level.PlayerChunkMap is in unnamed module of loader java.net.URLClassLoader @736e9adb)
at com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_21_R1.regen.PaperweightRegen.initNewWorld(PaperweightRegen.java:389) ~[?:?]
at com.fastasyncworldedit.bukkit.adapter.Regenerator.regenerate(Regenerator.java:116) ~[?:?]
at com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_21_R1.PaperweightFaweAdapter.regenerate(PaperweightFaweAdapter.java:561) ~[?:?]
at com.sk89q.worldedit.bukkit.BukkitWorld.regenerate(BukkitWorld.java:258) ~[?:?]
at com.fastasyncworldedit.core.wrappers.WorldWrapper.regenerate(WorldWrapper.java:278) ~[?:?]
at com.sk89q.worldedit.command.RegionCommands.regenerate(RegionCommands.java:712) ~[?:?]
at com.sk89q.worldedit.command.RegionCommandsRegistration.cmd$_regen(RegionCommandsRegistration.java:954) ~[?:?]
at org.enginehub.piston.CommandManager.execute(CommandManager.java:157) ~[?:?]
at com.sk89q.worldedit.extension.platform.PlatformCommandManager.lambda$handleCommandOnCurrentThread$16(PlatformCommandManager.java:727) ~[?:?]
at com.sk89q.worldedit.extension.platform.PlatformCommandManager.handleCommandTask(PlatformCommandManager.java:748) ~[?:?]
at com.sk89q.worldedit.extension.platform.PlatformCommandManager.handleCommandOnCurrentThread(PlatformCommandManager.java:729) ~[?:?]
at com.sk89q.worldedit.extension.platform.PlatformCommandManager.lambda$handleCommand$14(PlatformCommandManager.java:700) ~[?:?]
at com.sk89q.worldedit.extension.platform.AbstractPlayerActor.lambda$runAction$1(AbstractPlayerActor.java:672) ~[?:?]
at com.fastasyncworldedit.core.util.task.AsyncNotifyKeyedQueue.lambda$run$0(AsyncNotifyKeyedQueue.java:48) ~[?:?]
at com.fastasyncworldedit.core.util.task.AsyncNotifyKeyedQueue.lambda$call$1(AsyncNotifyKeyedQueue.java:58) ~[?:?]
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317) ~[?:?]
at com.fastasyncworldedit.core.util.task.KeyQueuedExecutorService$KeyRunner.lambda$run$0(KeyQueuedExecutorService.java:150) ~[?:?]
at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1423) [?:?]
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:387) [?:?]
at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1312) [?:?]
at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1843) [?:?]
at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1808) [?:?]
at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:188) [?:?]

I'm having a similar issue, but my error looks different.
! [Wed 15:14:24 WARN com.sk89q.worldedit.bukkit.BukkitWorld] Regeneration via adapter failed.
java.lang.UnsupportedOperationException: Regeneration currently not support on Paper due to the new generation system
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_21_R1.regen.PaperweightRegen.(PaperweightRegen.java:196)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_21_R1.PaperweightFaweAdapter.regenerate(PaperweightFaweAdapter.java:561)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.bukkit.BukkitWorld.regenerate(BukkitWorld.java:258)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.fastasyncworldedit.core.wrappers.WorldWrapper.regenerate(WorldWrapper.java:278)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.command.RegionCommands.regenerate(RegionCommands.java:712)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.command.RegionCommandsRegistration.cmd$_regen(RegionCommandsRegistration.java:954)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//org.enginehub.piston.CommandManager.execute(CommandManager.java:157)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.extension.platform.PlatformCommandManager.lambda$handleCommandOnCurrentThread$16(PlatformCommandManager.java:727)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.extension.platform.PlatformCommandManager.handleCommandTask(PlatformCommandManager.java:748)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.extension.platform.PlatformCommandManager.handleCommandOnCurrentThread(PlatformCommandManager.java:729)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.extension.platform.PlatformCommandManager.lambda$handleCommand$14(PlatformCommandManager.java:700)
at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.extension.platform.AbstractPlayerActor.lambda$runAction$1(AbstractPlayerActor.java:672)
at FastAsyncWorldEdit-Bukki

I'm having a similar issue, but my error looks different. ! [Wed 15:14:24 WARN com.sk89q.worldedit.bukkit.BukkitWorld] Regeneration via adapter failed. java.lang.UnsupportedOperationException: Regeneration currently not support on Paper due to the new generation system at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_21_R1.regen.PaperweightRegen.(PaperweightRegen.java:196) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.bukkit.adapter.impl.fawe.v1_21_R1.PaperweightFaweAdapter.regenerate(PaperweightFaweAdapter.java:561) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.bukkit.BukkitWorld.regenerate(BukkitWorld.java:258) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.fastasyncworldedit.core.wrappers.WorldWrapper.regenerate(WorldWrapper.java:278) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.command.RegionCommands.regenerate(RegionCommands.java:712) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.command.RegionCommandsRegistration.cmd$_regen(RegionCommandsRegistration.java:954) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//org.enginehub.piston.CommandManager.execute(CommandManager.java:157) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.extension.platform.PlatformCommandManager.lambda$handleCommandOnCurrentThread$16(PlatformCommandManager.java:727) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.extension.platform.PlatformCommandManager.handleCommandTask(PlatformCommandManager.java:748) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.extension.platform.PlatformCommandManager.handleCommandOnCurrentThread(PlatformCommandManager.java:729) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.extension.platform.PlatformCommandManager.lambda$handleCommand$14(PlatformCommandManager.java:700) at FastAsyncWorldEdit-Bukkit-2.11.0.jar//com.sk89q.worldedit.extension.platform.AbstractPlayerActor.lambda$runAction$1(AbstractPlayerActor.java:672) at FastAsyncWorldEdit-Bukki

Regeneration currently not support on Paper due to the new generation system

Yeah, so when will it be supported again?

When we have the time to do it, and want to do it