We very often see the same username created across many instances

Guilty as charged. I’ll say though, there are several legitimate reasons why one might want to do this. I personally use it as a substitute for Reddit’s multireddit feature, by grouping community subscriptions across different instances by theme. As long as users use the same username across instances I don’t think this practice should be automatically regarded as an attempt to sockpuppet. It that was the goal, the accounts would definitely not be using the same username across all the instances.

Thanks for that input, that’s very cool that those relays exist. I have to apologize anyway though because I apparently was pretty confused when I made the original post, because on Lemmy you can’t directly follow other Lemmy users at all, whether they’re on Mastodon or Lemmy.

Something like what I envisioned might still be workable, but it would take a bit more effort and savvy. It would probably require a Mastodon hashtag bot as well as a dedicated Lemmy community for each tag for the bot to post into. See my edited OP.

See my answer to @rowinxavier

This is what I’ve been doing to log into new instances, but it always seems to just replace the instance I was already logged into with the new one. The UI looks like it’s supposed to show a list of instances and the button says “Add account”, but the list is always empty, no matter if I’ve logged into other instances before.