I've got to say, from a professional software development point of view, what @MastodonEngineering is doing is really impressive.

I'm self-hosting using Docker and even upgrades like this to 4.2.0 is a 1-2 minute task.
1. Back up database
2. Pull image
3. Run one set of migrations by copy-pasting from the upgrade notes
4. docker compose down and up
5. Run second set of migrations
6. 🥳

It's been a looooong time since I've had any issues at all.

Well done, @Gargron, @Claire, @renchap, et al. 👏