Firewall settings fixed, Mastodon version upgraded. It's amazing how resilient my single-user instance was against operator error there.
My web interface was several minor versions behind the server, and I accidentally made my firewall settings much more draconian (the docker container could not make outbound connections, only answer nginx requests).
And yet the experience was still bearable enough I put off fixing things for almost two weeks.
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!