Brush effects not working?

P.S. The reason why your painbrush doesn't do anything is because all the sliders are set to zero. Check at the bottom of the panel. There is a checkbox to reset all sliders when you create a new mask. You probably have that checked.

When you select brushing, then the next step is to actually use the brush on your image. The area brushed should be covered with the proper colored brushing overlay. (if you don't see the proper colored brush overlay, press letter O)

Nothing happens to your image when you brush because you have not selected any edits. All sliders are at zero. As soon as you change the sliders, the overlay should disappear and then you will see the changed image (changed based upon your brushing).

I think that triangle was removed, and the Amount slider now always shows, because it confused people that the panel could be collapsed and the Amount slider would only show when it was collapsed.

By the way: https://support.apple.com/en-us/HT201361#:~:text=To%20take%20a%20screenshot%2C%20press,to%20save%20to%20your%20desktop.