2010 it was over
8%. 2015 it was
3.43%. That was 4.28 million Mac gamers. With 2.49% it should still be 3.11 million on Steam. Many people also only buy games on Mac App Store. There is also GOG, Epic, Ubisoft and Origin. It's clear that many play mobile games but 3-4 million is still a large customer base. The average game sells only
32 000 copies and developers talk about 30 000 to 50 000 sales to break even. 3-4 million additional customers should be a good market to invest in.
Slowly but surely more games are being ported to Apple Silicon but native games are available mostly through Mac App Store until Valve decides to support Steam for ARM64.
According to
https://www.applegamingwiki.com/wiki/Home there are 31 native ports, but not all games are on that list. Some games with native support are Myst, Asphalt 8 and 9, Total War: Rome Remastered, Baldur's Gate 3, Disco Elysium, Total War: Warhammer III, Path of Exile and EVE Online.
I think things are going to get better when M1X comes out next month with 16-32 GPU cores.