Porting games is a different story but it does not change my point. Most games are developed from PC, not Mac and then they plan to port it to Mac. But still, only few of them ported to Mac and dont expect any major online or AAA games for Mac at this point.
Yes, most games are either ported from PC or are actually made with cross-platform in mind (when you use an engine such as Unity). And yes, games that require fast hardware are often not ported (for obvious reasons). As to "major online games...", lets look at what internet claims to be some of the most popular online games in 2020 (in no specific order):
- Fortnite (has a Mac version)
- PUBG (no Mac version, but iOS version — runs on Metal)
- LOL (has a Mac version)
- Hearthstone (has a Mac version)
- Splatoon 2 (Switch exclusive)
- Minecraft (has a Mac version)
- CoD (has a Mac version)
And let's add some popular/well known MMORPGS
- WoW (has a Mac version)
- Destiny 2 (no Mac version)
- GTA V (no Mac version)
- Elder Scrolls Online (has a Mac version)
- Guild Wars 2 (has a Mac version)
- EVE online (has a Mac version)
- RuneScape (has a Mac version) — wow, people still play this??
As you can see, it's not perfect, but also not too shabby considering the "3% market share"