I'm not upset at downvotes. My comment got plenty of 'em. It's fine.
If the meaning of them is so individual and nebulous, then I'm even more mystified why anyone would hand them out. You dislike something, but so what? What's anyone supposed to do with that information? They can't be interpreted as anything apparently. Lemmy's userbase is too shallow and it's sorting algorithms too unsophisticated for anything to get buried. So it's an action without a goal, a petulant thumbs down that in most cases just leaves someone puzzled as to why it happened at all.
It might have been https://sub.rehab that was mentioned (you can migrate using their Settings page apparently). Their FAQ also mentions alternative sites (mostly just big static lists by the look of it).
Or it could have been an app - Voyager for instance will take a big list of your subscriptions as a MultiReddit and sub you to Communities with the same name.