Even better if this could be a lemmy feature I think, but client-side would be good too

I would love to have this too. Big and active communities drown the less active ones and I would like to have different groups of topics to be able to not miss those less frequent posts.

Either way sounds good. Is this a feature already in lemmy or Sync?

Even you asking this question means you should not. Systemd is perfectly fine for most people and the people that dislike it have their very specific reasons. Just use what your distro gives you, you shouldn’t have to care about these things.