You are writing of via stitching as it would be a check-box applying it for the whole PCB. I have never seen such check-box and here I have only KiCad V5 (because of Win7), so can’y check anything.
I am placing vias individually. The other way I know (but never tried) is to place array of vias. I believe doing it you (and not KiCad itself) decide where and how many lines/columns of vias you want to place.
I often use the area outside the PCB as a scratch pad for temporary stuff. From text notes to sorting footprints, saving layout snippets etc. An easy fix is to:
Place 5 or so vias manually on a suitable grid (I.e 5 clicks after the function selection).
Copy those 5 and paste it 5 times. (30 vias)
Copy again, and paste again 5 times. (180 vias). You get the idea.
From that, you can then copy or move a bunch of them to wherever you want them on the PCB.
But do practice a bit in the beginning. Via net names can be automatic or manual, and you have to know the difference.