A user mentioned that copper hopper is incompatible with lithium, or at least requires mixin.block.hopper=false

This is not intended and will be fixed in Lithium: CaffeineMC/lithium#411

I only created this issue report to inform you about it, I will post again when a new version with a fix releases, so you can give feedback whether the issue persists.

The latest lithium build from https://github.com/CaffeineMC/lithium-fabric/actions/runs/3373824762 seems to work correctly with Copper Hopper's item filters in my testing, however I am not experienced with the details of copper hopper's features, so I recommend test it yourself as well.
The fix will be in the next lithium release

Oh, fantastic, thank you! I just assumed it was a mixin conflict that could not be easily resolved. I'll update the docs and tell people to upgrade to the latest Lithium when it's out.

Thanks!