I wrote up a rough guide to upgrading from Sentry 9 to Sentry 20, since I struggled with the upgrade myself. Importantly, I added some config tuning options to turn on, to make debugging easier. Hopefully this makes it easier for anyone else doing the on-prem upgrade.
But just as a note on this part:
I would recommend automating this to run weekly after hours from your CI platform of choice.
That could be a bit more complicated than you wrote above. “Docker down || install.sh”, you need to pull updates from the repo (thats easy enough to automate). Remember tho that if you use Master you will run a nightly version.
You also need to merge .config.example.* into your existing config.