Hi I also have the Nik Pluggin issue on my new Mac - ie the plugins do not execute when called from Affinity Photo.
Background. Up until recently running an old MacBook Pro on Mojave. Affinity Photo and Nik Collection 3. All worked fine (albeit a Nik was slow)
Had to make the move to a new M1 Mac mini with Big Sur. (11.2). Running Affinity Photo (1.9.0) and Nik Collection 3. Affinity Photo runs fine. Nik works if opening independently and opening photos from drop down menus within. Affinity photo it appears cannot invoke Nik Collection even though all appears under filter option as expected.
I raised a ticket with DXO re Nik Collection a few days back and this was the response I got ...
"Thank you for writing and for your question. We are making every effort to resolve the compatibility issues when using Nik Collection 3 with Affinity Photo on a Mac OS 11 Big Sur system. At this time, we have not yet isolated where the incompatibilities exist, so we are not sure if this is an issue with the Nik Collection or with Affinity Photo. Please be assured that we will try to resolve this issue as quickly as possible.
"
So they seem to be aware that there is an issue but need to work with Affinity to resolve. I hope both parties are talking to resolve
Hopefully a frustration relieving fix soon !?