I was having an issue on a new site build and then replicated the issue on a fresh WordPress installation.
All I have installed are the two latest Meta Box plugins (Meta Box v5.6.18 & Meta Box AIO v1.20.2) and the latest Default WordPress Theme (Twenty Twenty-Three v1.1) all on the latest WordPress version 6.02.
I added a WYSIWYG custom field to both Pages & Posts. However, I am unable to enter or see any data in the Visual tab or the WYSIWYG editor. The Text tab does work and I am able to save data. However, it is not visible or editable in the Visual editor.