Looks like this is totally broken now for me on Catalina with the latest betas😧
In current retail v2 apps and previous betas with pixel brushes;
Control+Option+Click&Drag Left/Right = Brush Size.
Control+Option+Click&Drag Up/Down = Hardness.
And with Vector brushes: Control+Option+Click&Drag Left/Right = Brush Size.
Now in all beta 1736; Shift+Control+Option+Click&Drag Left/Right = Brush Size. (the Shift key is now need too??)
Control+Option+Click&Drag Up/Down = Hardness. (unchanged and same as before)
And with Vector brushes: Control+Option+Click&Drag Left/Right = Brush Size. This still works, however immediately afterwards the brush outline and crosshairs disappear 90%+ of the time and you have to click the canvas again to get them back.