The service provider updated the underlying PHP installation, to 8.1.1
This weekend the Basel theme stopped functioning, with an fatal error get_header(). If this is rem’ed out then other functions also fail. By doing an include of inc/classes/Layout.php some functions started to work, however, other functions, continued to fail. these changes have been removed, just for testing.
All plugins have been removed and added one at a time, however, no difference was seen.
If the theme is removed, the system uses the default theme and at least access to the admin area can be seen.
Have attempted to restore from previously known working environment, however, no dice.
Now we have re-purchased the product for support, I will attempt to freshly download Basel and apply it and see what that results in.