Apple Photos - Launch issues in macOS 11 Big Sur
If you are experiencing difficulties launching ON1 as an Extension from within Apple Photos in Big Sur, double check some settings that need to be enabled in for the ON1 extensions to launch properly.
In Apple Photos, click on the Extensions tab, then Manage.
Make sure that ON1 is correctly enabled in the Extensions.
You'll also want to make sure that ON1 apps have Full Disk Access in the System Preferences> Security & Privacy settings.