Upgrading from 2.9.0.beta8 broke the site, unrecoverable

[JammyDodger]

There are also some good pointers on how to manually update from the server in this topic:

Manually update Discourse and Docker image to latest

If you self-host Discourse, you occasionally need to run a manual update via the command line to get the latest security releases newest libraries. These updates are not picked up in admin/update, which is why you’ll occasionally need to do this additional step. Discourse itself should be updated about twice a month, by clicking the “Update to Latest Version” button in your admin dashboard (admin/update). Every two months we recommend SSH’ing into your web server (using putty or your favor…

A ./launcher rebuild app can often be a good Plan B, and if you get any errors during that you can scroll up and have a read.