Hallo Thomas,
now my computer has returned from Apple branded service, stating that it is perfectly fine. Load tests were performed, error messages were checked, a factory reset was performed, and Big Sur was reinstalled. I checked the operation of other necessary applications (Final Cut Pro X, Compressor, Motion), which I use for work - without problems. After installing Affinity Photo still the same result. The application does not start at all (rainbow wheel) until the start of the set stops (the application does not respond). It's incredibly frustrating, I've been using it for a long time, suddenly this ... The Mac Pro from 2014 isn't old, I think. I don't know who to contact. 😞