Version Info

• Minecraft, 1.20.1,forge 47.3.0 or 47.3.22
• Fusion, 1.1.1-works,1.2.0+1.2.1 crash

no optifine/whatever,just 3 mods:
fusion-1.2.1-forge-mc1.20.1.jar DimStorage-1.20.1-8.0.1.jar EdivadLib-1.20.1-2.0.1.jar (tried one version down on dimstorage,no go)

Steps to Reproduce
just launch and wait(myself using gd launcher)

Crash report (~/logs/latest.log)
https://gist.github.com/Korenchkin/ec2b585f29c70301b8126ae14d89e4a6
https://gist.github.com/Korenchkin/8191aa83bf7b39128cb2619cddb08dc0

no spaces/bad characters in path
"C:\Users\Korenchkin\AppData\Roaming\gdlauncher_carbon\data\instances\Korentest\instance"

i think (my) win11 still uses cp1250 i've read in some logs,at least some(legacy) apps?czech republic locales here...

and another info,not sure,just posting it here since some user shared this somewhere(too long searching,lost track) about similar/this problem,might help:
https://stackoverflow.com/questions/11063102/using-locales-with-javas-tolowercase-and-touppercase

thanks,
k.

I got a crash with same error.
Forge: 47.3.12
Windows 10 with Swedish locale (if that is the issue).

This has been fixed now in version 1.2.2 of Fusion.
Thank you for reporting the issue!

Can confirm that it's working!