I’m having a few issues with the customizer with shapely. All my plugins, software, etc. are up to date. At first when I clicked on customizer it would just be a blank screen. After a bit of reading I saw that some plugins might conflict so I turned a couple of page editor plugins off. It goes a little further now to this point (attached picture) but that’s it.
You have 404 error on some files, this means they are not loading from the server, try to reinstall theme and check again, you should not have 404 errors
No matter what I did I couldn't get the errors to disappear so I took the day to re-install the software from a backup in early July. I did the backup, then updated all the software. All seemed well until I tried to customize the homepage pictures. I would get the blank white screen again. I deactivated element or and page layer editors and this got me a little further. To the same spot I originally attached the screenshot. Also this messed with my menus. I re-activated Elementor and Pagelayer and the webpage came back to normal however, I'm still not able to customize.
What happens when you disable all third-party plugins? Especially page builder plugins?
If the customizer works on deactivated plugins then temporary disable them, customize the theme and then activate those plugins once you finish with customizer