I never knew about the double tap outside a selection to deselect gesture. The way I do deselection, which I find faster than any methods mentioned as alternatives here, is to put deselect in the quick menu and then assign quick menu to double tap in the prefs. Then all you have to do is quickly double tap wherever your finger happens to be, then tap the deselect button from the quick menu, which will appear right near your finger. You don’t have to dig into menus or even reach up to the toolbar.
I encourage you to try it out icezimy- it’s not exactly what you were asking for but it’s really quick and better than the other methods imho. I was struggling with deselect feeling cumbersome until I tried this. And it’s awesome to put more stuff in there too. If you are working with lasso a lot, putting fill with current color, clear, and hide selection in the quick menu is very convenient and can speed things up a lot. I even put buttons to open the color, layers, and brushes panels in there. Really improved my experience with the app.
I can see how double tapping outside the selection to deselect would be quick and nice to have working again in all the selection modes. I’m not aware of what would be making it not possible. I’d personally still set my double tap to the quick menu (which I think simply overrides that behavior, which makes sense to me) and do it this way, just for all the benefits you get with quick menu on double tap.