I have placed soothing lanterns in every chunk of my vanilla enderman farm, yet eldritch endermen still spawn.

I've updated the mod to a newer version of fabric API and the soothing lanterns appear to be working properly now. Also, the soothing lantern does not rely on the code I commented out, so that shouldn't be the crux of the issue.

I'll be doing a few more bug tests before I release the update, and hopefully, that fixes your problem.

Fixed in the latest release.

Update, looking at the code it is all commented out so it works nowhere.