Paint random tiles in a big square/grid, RandomBrush doesnt do what it says on the lid

I just want to create a large grid say 1000x1000 toiles, using the paint bruish tool inside the tilemap pallete, simply just painting random tiles into my tilemap, why is this not possible??

When I use the grid tool to paint with the random brush in a big grid, it just repeats the same pattern a million times,there is absolutely 0 randomness, its just painting a pattern like the default brush does, why is it called the random brush if it doesnt do anything random?
selectedRaNDPMtOILE

Obligatory XKCD:

Just googling for random tile in Unity gives me nothing useful, just random procgen stuff, so perhaps you could refine your question to include a link to the documentation related to what isn’t working for you?