So I fired up Firefox, browsed around and was quite happy with the experience, and then logged into OLD.reddit.com. (I can't stand the new UI).
After some "messing around", my account was suspended, with this message:
Evading your ban in r/... from 2023-09-29 on a connected account. Moderators get to decide who can participate in their subreddits. Using alternate account(s) to circumvent a subreddit ban makes it more difficult for moderators to effectively run their communities and is a violation of Reddit's rules.
Yes, I was banned from a subreddit. And that was by bad, and is totally OK. Three weeks later I was banned for using a different browser, with no reason given.