I'm not sure whether the mod is genuinely incompatible with Rats 8.1 or if it's just a dependency issue. But right now the game straight up refuses to load due to declared dependency version.

[main/ERROR] [net.minecraftforge.fml.loading.ModSorter/LOADING]: Unsupported installed optional dependencies:
Mod ID: 'rats', Requested by: 'totw_modded', Expected range: '[8.0.6,)', Actual version: '1.20.1-8.1'

I get a similar message

[main/ERROR]: Unsupported installed optional dependencies:
Mod ID: 'rats', Requested by: 'totw_modded', Expected range: '[8.0.6,)', Actual version: '1.20.1-8.1.1'

Looking forward to updating, but intil this is fixed I'll be in version 8.0.6. Thanks, Devs!

Can confirm I have the same issue on my end:

When launching the game with the new Rats 1.20-8.1, I get a crash.

Here's the link to the mclo.gs log

Log error is ...

Error during pre-loading phas
net.minecraftforge.fml.ModLoadingException: Mod totw_modded only supports rats 8.0.6 or above
Currently, rats is 1.20.1-8.1

I can also confirm rats 8.1 and 8.1.1 are incompatible with TOTW: Modded.

I will try and test to fix.

New patch is out with the fix to be used with the newer Rats version

The fix should be out now! :)