There are so many workarounds and all of them are completely insane and even with a ton of steps, don't work with picture in picture videos unless they're rectangular.
Literally just need a "Add stroke" or "Add border" effect where you simply pick the colour, and and pick the thickness of the frame / border.
So simple. Thousands of us want it, and have done for a long time.
Surely cannot be that complicated to do?