Help! C-7 Error 500 After Update. Unable to Do Anything

Try these steps below. To revert to 2.3.7 it is in the "Advanced" menu.
For the debug disable endpoint, the main platform needs to be booted.
You can also try booting up fully without restoring from a backup, just to see if that works without issue. Then you can try to load a backup using the UI at Settings > Backup .

If you can get it working on 2.3.7 then you could try updating back to current 2.3.8.140

Might not be a bad idea to get the latest diag tool also:

Navigate to http:// [Your Hub IP] /hub/cloud/updateDiagnosticTool , wait a few minutes (you will not see a progress report), and the latest Diagnostic Tool version will be downloaded if needed.