My estimate is that Lightroom use on Mac now outnumbers Windows by 2:1.
This is based on visitor statistics to this site which show 51% Mac, 25% Windows. The balance of 20% iOS and 3% Android is impossible to split between Mac and Windows users, though I’d expect the ratio would be similar.
While these are only visitor statistics, I think they are representative of Lightroom users, After all, if you aren’t a Lightroom user, you’d be an idiot to visit this site!
That said, I don’t think such numbers are a basis for deciding which computer brand you should buy!