Not sure how complex this might be to implement, but it might be good to look into fixing the issue of:

If I'm logged into say piefed.social and I see a link on another forum to a post on piefed.ca, when I click on it I'm not logged in, and then I can't upvote or comment.

Meaning I need to go to piefed.social and search for that post if I want to interact with it, which is a lot of friction.

Perhaps if you go to a piefed.ca post it can look at your cookies to check if you're already logged into another piefed instance, and then redirect & open the post through the instance you're logged into.

Or have a big redirect button that offers to redirect you to the post you're looking at but in the instance you're logged into.