This looks like it will turn into a complex upgrade. I was about to pull an all-nighter and upgrade everyone on Masto.host to Mastodon v4.0.1 but v4.0.2 was just released https://github.com/mastodon/mastodon/releases/tag/v4.0.2
I will pause upgrades now because there is no point in forcing myself to do an all-nighter for something that I need to do tomorrow again.
So, tomorrow I will upgrade the servers still on v3.5.3 to v4.0.2 and then upgrade the ones that are already on v4.0.1 to v4.0.2.
Sorry about that.