Mod Loader (Required)

Fabric

Minecraft Version(s) (Required)

1.21.1

Mod Version(s) (Required)

v21.1.1

Other Mods Involved (Required)

Yes

Notes (Required)

To be real its probably just a conflict with one of the 400ish mods.

Your other mods like easy anvils and overflowing bars work fine.

When booted up with just block runner and dependencies it works fine.

The steps:
1- Boot game with gazillion of mods.
2- Click single player
3- Click create new world (if other worlds already present)
4- IF its crashing you will see saving world
5- Game crashes stating: UnsupportedOperationException related to "java.util.Collections$UnmodifiableMap.clear" and "NeoForgeDataPackExtensionsFabric.java" I think.

Here's a link to the mod list but just in case you need it.

And a heads up I'm not used to using git so if I've done something wrong, my bad.

Crash Report (Required)

https://gist.github.com/CptJackspacker/07f7bb4947434cee086d652e6759148b

latest.log (Optional)

https://gist.github.com/CptJackspacker/e1aa269f47d5c0edfdc84c9904b96a17

Please follow these instructions, the class I need from you is class_2370.

Fuzss/betteranimationscollection#32 (comment)

So I did follow the instructions but I got two classes which don't match the class you need which are class_310 and class_5762

Please try the new v21.1.2, does it fix your issue?

The new version worked thank you!