The one difference to keep in mind is that each community (the subreddit equivalent) and each server (the equivalent of a 'site' like Reddit) have their own sets of rules and mods. So when you post to a server that's not your home, just be aware you are subject to those sets of rules in addition to your home server. You should be fine for the most part if you act with empathy and respect, but no need to take it too hard if a mod informs you that you broke a rule.
Lastly, don't be afraid to post/comment in niche communities with a small amount of activity, but it's a good idea to do a community search (under "All" filter) to check if a more active community is present on another server.
Lemmy instances are in the middle of transitioning to a new version (0.19.x). It's been a bit bumpy. You might notice some changes once this instance upgrades. We've been holding back until we're confident that the new version is stable.
lemm.ee was in a rough spot in the couple weeks after their version update, but they got it figured out and it's been good since. Maybe this is me being naive but most of the major instances should have that behind them by now I think
You should know there are multiple free clients you can use to view content in Lemmy. Try a few and select one you like. I recommend using one that provides the ability to block specific instances, communities, and users. It will improve your experience and reduce frustrations.
A lot of Star Trek is quite good. If you watch TNG, start from season 2.
Several distros work absolutely fantastic on older Intel-based Macs; Mint has a knack for breathing new life into old hardware. Can't speak from experience about the ARM-based Macs.
List of communities you see from your instance is just the ones subscribed to by an existing user. You may still find a niche one and have to be the first to manually subscribe.
It used to be quite far left, back when tankies were everywhere. Now it's pretty tame, though you'll still run into literal socialists/communists from time to time. It's about where Reddit was when I left, so par for the course.
I consider myself libertarian, and it's honestly not bad, and I like ragging on conservatives anyway.
You can tell Hexbear is super communist by how much they simp for Putin, an unashamed oligarch who's so reactionary he gives Desantis wet dreams. The Lemmy instance where horseshoe theory has been hammered into a circle.