Hi there!
Maybe the same problem here: I've added several ICC Profiles to my macOS system folder. These profiles are showing up in any DTP software but not Affinity Photo/Designer/Publisher.
If I open an old document that was assigned one of these newly installed profiles, this one profile will be displayed in all Affinity programs in the future.
For example:
I've installed the ICC profile "PSO Uncoated V3".
It doesn't appear in the Affinity programs.
An old document uses ICC profile PSO Uncoated V3.
If I open it, the profile suddenly appears and can be used, even for future documents.
Same problem on my iMac and Macbook Air, both running Big Sur 11.0.1 and the newest App Store Affinity software.
Jan