I’m asking because I used to run into the maximum number of blocks on my Reddit client
I think they used the multi-reddit list as the back-end for subreddit block list. I too ran into the limits.
I don’t think Lemmy has any limit, but performance will likely degrade and it is entirely possible that your personal block list causes overload of servers with lots of data in them.
I imagine they must have some limit, otherwise that would be an easy exploit, just creating a practically infinitely long block list to crash the instance. I would get it if clients have an unlimites blocklist, but not instances.
If that’s the case, wouldn’t it make sense to put a genre/label onto sublemmys? Because e.g. I block all “bread for the people” subs (i.e. sports). And being able to block “sports” would be much easier.