You saw it in the video, but you missed it said (for macOS only).
Well, even with macOS, there is a better option, and for Windows it is the only option anyway.
You do not create the selection mask in the SRDx for Photoshop plug-in itself.
Instead you create a mask in Photoshop, which offers more options for different selection masks.
When you call SRDx, the selection mask is carried over to the plug-in, and will be used here.
In case you want to have different masks for different SRDx parameters to optimise different parts of the image, you can repeat this process:
Create mask, call SRDx, set parameters, optimise and close plug-in, create new mask, call SRDx, set other parameters, a.s.o..