Applying last security patch from 2020 broke my High Sierra (WindowServer will not launch)

I wanted to renew my macOS Server certificate. This failed to work (last time I did this was Jan 30, 2024, when it still worked.

I suspected certificate errors, so in an attempt to get newer certs I installed the last security patch for High Sierra. As a result, my Mac will boot (many processes are running, I can ssh into it), but the WindowServer won't start because the signature on it fails.

Is there a way to turn this off so that at least I can get a loginwindow and log in using the GUI?

Reinstalling the OS is a next option, but I recall from the past that cost me everything related to Server.app, and as using Server.app is my goal, this is not an option to try yet.

Another usable option would be if I can renew the certificate from the command line. I'll put out a separate question for that.