@SchrodingerCat thanks. I tested the tool with your image. My guess is that you actually changed the mode, but I may be wrong.
If I use the “regions of specific color” with white as a color and make a enclosing region similar to the one in your videos, then everything inside the lines is filled. On the other hand, if I use the “regions surrounded by specific color” with black, then only some regions are selected.
The “issue” I think is that this tool doesn’t take the image borders as a boundary, like csp seems to do. This means that what is outside the image is considered transparent. If one uses “regions of specific color” then all the white regions are selected because they are inbetween the black lines and a transparent region that is outside the image but inside the enclosing shape, so they are considered closed. If one uses “regions surrounded by specific color” then some of the white shapes are not totally surrounded by black because they are next to transparent on the bottom, so they are not considered closed an they are not filled.
At least that’s what I think is happening.
So, my question to all of you is: should the tool in Krita behave like the one in csp and take into account the image borders? I didn’t do it that way because the layers’ contents can extend ouside the image bounds. But maybe here is better to have it like csp.