Not all apps eligible for focus mode?
Focus Mode cannot be enabled for certain apps, such as Things3, Affinity Photos, Affinity Designer, Affinity Publisher, Parallels Desktop, Nova. I cannot select them through settings, they are not even in the list. They show up in the Menu Items 'Focus Mode Apps' list, but are not able to be selected that way either. Enabling a global hotkey and using that does not do it either.
At first I was thinking it was apps that were not purchased through the App Store, but Things 3 was purchased through there.
Unfortunately those apps are the core of what I need to stay focused on.