I do not use Setapp. I have many of the apps, but have purchased a few of those prior to Setapp’s appearance on the scene. Taskpaper is one of those.
I have a Taskpaper 3 license purchased some time ago. I have entered this in my installed version of Taskpaper 3.8.6. It launches OK from Alfred or by opening it in the Applications Folder, but I cannot open it by double-clicking on .taskpaper files in the Finder. Nor can I open file links ./file.taskpaper from inside Taskpaper itself. This is the message I get when attempting that.
This copy of TaskPaper cannot be launched without a Setapp account.
It seems that the Setapp check is taking place when it should not.