@Joanna & all
I tried this now with PL 9.1.0_488 (Win) and NVidia driver version 581.57
on a tif-file that I had made a few years ago.
shown here with AI option “Add selection” / the same with “Area selection”
= clean masks / selections
.
and here with → mouse pointer over the individual submask symbol
e.g. to control the spread of a negative / subtractive mask