Say, I have account here on kbin.social and get permabaned, does it mean that I can not login at all?
If you get banned from all of kbin.social, yes. It's like getting a Reddit suspension. On the other hand, if a community like Technology@beehaw.org bans you, you just can't post there, but can still post other places, like a normal Reddit ban.
I think you could still post on other beehaw communities if you're banned from Technology, or other Kbin ones if you were banned here, but I need to confirm that. That's how it should work, anyway.