I’m wondering though why the implementation is like this. What if a person wants to select some decks but drawing a rectangle puts other decks in it too? The simplest situation where this happens is if the masks to be conjoined are in the three axis of a triangle and some other mask is in the centre of that.
On Anki Desktop, you can also select multiple masks by clicking on the first mask, then hold the Shift key while clicking on each additional mask you want to combine.
Edit this one on desktop instead? Don’t add the mask in the middle until you’ve added the masks around it and grouped them?
As for why it’s implemented like this – I assume that drag-to-select is the easiest to implement because that’s a fairly standard method for multiple-selecting on touchscreens.