first of all respect for such an achievement. A lot of work with good documentation and functionality! As a test I created the page: https://www.medewa-hygiene.de/testsuche/
I have following questions:
Can you deactivate all filters per group in the frontend with one click? Are everyone always active at the beginning?
I was having trouble with the search results page. The Divi Builder has a template for the search that I had to disable. Actually, the layout (Divi shop page): https://www.medewa-hygiene.de/artikel/ should be used.