Log: https://pastebin.com/PdMvWeFE
configured-neoforge-1.21-2.5.0.jar
Neoforge: 21.0.86

I get the same error and my logs look pretty similar.

the config directory is used for the default configuration (NeoForge)
The is no more nightconfig

Can confirm the same bug on 1.21 aswell, with included logs: https://mclo.gs/qPkySAT

I'll have a fix out soon. NeoForge made some changes to their config system.

I'll have a fix out soon. NeoForge made some changes to their config system.

when's soon?

Just because the code of NightConfig update for this change

Yup, 1.21 crash

https://pastebin.com/ZfR0YgGm

same exact thing, dont wanna switch to forge either cuz i use mods that are on neoforge but not forge
edit: found a work around for now switch to neoforge v21.0.81, not fully tested yet but its gotten me ingame
most mods no longer work on this older neoforge version so even tho it fixes the issue with configured it causes incompatibilities with most other mods

still happening, hopefully gets fixed soon.

Any updates?

any update in this issue, its still happening.

Hi happens to me too, are there any alternatives to configured I can use in the meantime ?

Hello there :-) Any updates?

Still happening :(

Give the man a break. I don't think you realize how hard it is to deal with Minecraft Modding. Minecraft isn't built by default to be modded, even though Microsoft says it is. And Neoforge is still trying to iron out it's own bugs. It's a pain in the butt all the way around. The issue was opened in July. Give him a chance to look at the error and debug, which takes awhile. And depending on the amount of time you have available dedicated to modding, you might not have time to sit down and do an extensive Debugging session. Sheesh.