Ok, this was weird...
After the upgrade something went wrong and Mastodon didn't work any more over here.
It took me a while fiddling around with errors, reinstalling ruby, bundle install and such things.
It looked similar to https://github.com/mastodon/mastodon/issues/15751 but I'm still unsure if I hit that issue.
However, Mastodon seems to run again now and I'm sorry for the downtime.
All friendly creatures are welcome. Be excellent to each other, live humanism, no nazis, no hate speech. Not only for nerds, but the domain is somewhat cool. ;) No bots in general! (only with prior permission). ---