theme option – “what we do” is not working anymore

I didn’t want to use the “costum” but the “page” mode in this section. When I added a page, the preview on the right side changed (narrow display) and at the end a wordpress error was pointed out.
I was able to reverse the problem at first, by using the “disabeled” mode. But since then I can no longer edit anything. When I switch to the “home page” display, or another that is not “disabled”, nothing is displayed in the settings area except a grey empty field.
How can I fix the problem?

Greetings

Stefan