I do editing with Audacity on a mac (and sometimes on linux).
With MacOS Mojave editing was a real pain. The program would only run sensibly when windowed. Through various investigations it seemed that the smooth running was dependent on resolution (we’re using a high res monitor). Don’t ask me why.
There’s a simple fix that worked for me: run the program in low resolution mode. Go to Get Info (command-I) on the application (in application folder) and check the box in the window that pops up
This seems to have fixed things. No idea why it’s an issue in the first place, but I can now do editing full screen again.