I tried it yesterday and as far as I tried it worked. I worked with the following extensions from photos, Develop, retouch and edit in Affinity. I could open, work, save and close. It transfered back to photos and I could save there. I have not tried the other extensions as yet.
I do have problems with opening (raw) photos directly from Affinity from the Photos library. I get a message that library is being loaded. Then I get a very short flash of thumbnails, which disappears. After which nothing occurs.