I spent months analyzing different ways of implementing masks/clipping masks and thinking how to implement that.
In my opinion the biggest limitation of masks in apps like Affinity/Photoshop etc is that mask can be only "raster" type.
In my solution it is solved. After i will add option to use groups as mask/clipping mask there will be no limitation.
I don't want any "special" masks.

Besides in version 1.1 there will be option to "Add mask from selection" which will make adding mask faster

Please send me that brush here or to info@luckyclan.com and i will check what is going on

Aux stamp is supported only in Paint, Pencil and Eraser tools, and it is ignored in Wet Paint, maybe you are trying to use it in Wet Paint tool?

For version 1.1 we added option to “load canvas into brush”, also from other layer.
It will allow to paint like this:
https://m.youtube.com/watch?v=Vcz5Fh6Wcx4

I will consider adding it to Select tools options.

Clipping mask - you can also open layer details in Layers popover and set mask/clipping mask there. I will think how to simplify that

Deselect - the are 2 more options:
- double tap on any Select tool icon in left toolbar
- activate rectangle/ellipse select tool and tap anywhere on canvas outside current selection

Yes, it will be added in version 1.1. We are going to publish it in about 3 weeks.

Mountain Lake