I wouldn't call this changing a default. If this were windows and my only option was 1) Petition the developer to rewrite their app 2) Buy more hardware 3) Edit the registry...
I would not consider that a mere change to the default.
There is no guarantee the work arounds will continue to work and it's asinine to have to rely on a playback card - which doesn't work on the M1 Mac's anyway.
- The app outputting video can use an OS-level API to capture and fully control the external display.
- The Mac owner can use a playback card to output a clean video stream.
- The Mac owner can use their root control of the machine to disable the dot. (A short script to do so is currently the top comment.)
So really, Apple has not taken away rights here. Clean video output is still possible. They have changed a default, though.