Grey Screen Customizer problem

Hi,
I have a problem with my customizer, since I’ve updated to WordPress 6.0 – I’ve updated all the themes and plugins, and also the WordPress version.
I’m using the newest version of Cologmag and various Plugins.

I’ve also created a second database where I tested switching off all the plugins and all the themes (I’ve tried using all the other themes) but nothing helped. I’ve also tried to reset the customizer with a third party plugin in my testing-database but unfortunately nothing of all the above mentioned steps helped getting the customizer to work.

I’m stuck with a grey screen and can’t do anything else but exit the customizer. I’ve searched for workarounds the last few days and tried various different options such as updating the PHP – and setting the PHP cache higher, but non of the options helped unfortunately.

How can I continue with this Problem? Do you have any idea how to fix it?

Thank you so much in advance.

Kind regards,

Faruq Nanouche
TRUST Mannheim