i am playing the java 21 version of gregtech new horizons together with some extra performance mods.
all of them paired including falsetweaks work flawlessly on a java 8 instance of the modpack.
i tried changing everything in the provided config of falsetweaks and changing everything to false the game actually starts but will crash upon world generation.
it is definitly falsetweaks that is causing those issues, without it the java 21 instance starts properly.

i will submit one crash report regarding the starting issue and one regarding the world generation/join issue and my modlist.

starting issue: https://mclo.gs/toTE8U0

world issue: https://mclo.gs/By7Cf6D

modlist:
GT New Horizons 2.7.2 I Java 21.txt

i would love to use falsetweaks again, the tweaks really change crucial parts of the game for me

For some reason you have weird files in your mods folder that are confusing my mixin loader, please remove them:
C:\Users\********\AppData\Roaming\PrismLauncher\instances\GT New Horizons 21\.minecraft\mods\CoreTweaks-master\gradlelibs\optifine-dummy.jar
C:\Users\********\AppData\Roaming\PrismLauncher\instances\GT New Horizons 21\.minecraft\mods\CoreTweaks-master\gradlelibs\fastcraft-dummy.jar

you shouldn't have mods extracted as directories in your mods folder, or any kind of git repos

the crashes still happen after removing those files

send the new crashlog