Looks like you are back so will attempt my question here.
The update to WP5.9 has corrupted the Appearance/Customize; Appearance/Header, Appearance/widgets.
It looks like it is theme related according to WP support. I have another site using the same theme for which I have NOT updated to 5.9 yet, thankfully, and it is still working fine on theme version 1.3. using WP 5.8.3.
The site with the problem is theme version 1.4. WP5.9
I don’t see that the most recent update 1.5.2 addresses this problem so I won’t proceed with that until I hear from you.
I would put a screen shot but it seems that is disallowing the ticket from going through.