I'm using Lightroom CC v11.1 on a Windows 10 Pro based (v21H1) desktop computer with lots of storage.
Initially I loved the new masking features. But now I'm having issues.
When I make a selection, it inverts it automatically. Then, whether I leave it as is or invert it back to what I originally wanted, any changes I make are made to the entire screen, not just the selected or not selected areas.
I originally noticed this when I tried selecting the subject. Since then, I've tried the brush and both gradients too. The same thing happens. Below is a print screen of a photo with the subject selected.
In your screenshot, notice that you have clicked on that disclosure triangle when in the mask adjustments panel. as a result, the adjustment panel had been replaced by an amount slider. Click on it again to revert back to the adjustments panel.
Oh, and you are showing the Presets panel, it would be helpful to see the History panel instead, minimize the presets panel, minimize all panels on left except history panel.
See the encircled (in red) disclosure triangle in the following image:
Also, in your screenshot the mask in use is minimized, we cannot see what brush has been applied, you may want to re-post your exemplar.