Just wait for when Apple removes OpenGL. Probably 90% or more of existing games will break unless their middleware can be recompiled for 64bit+metal.

The middleware that matters has supported Metal for about two years now.

Removing OpenGL isn't far away, as one of WWDC 2019 talks was exactly how to migrate to Metal from OpenGL, while all Apple frameworks now use Metal by default, although some of them still offer the old OpenGL support as fallback.

Middleware might have Metal support but not be used by the game nor tested. And not everyone is going to redo testing and QA on niche backend.

iOS gaming is bigger than desktop Linux....

and smaller than other platforms for the users of such middleware - and due to physical and power differences isn't usually running the same game but a modified one. A lot of porting to Mac depended on OpenGL being an API that you could start debugging on other platforms as well.

Something else worth mentioning is how most major game engines and several game vendors have had native Metal support for some time now.

This mostly benefits new games. If you want to update to (for example) Metal-compatible Unity, that probably means updating to the latest release, and bumping forward from 2017 Unity to 2019 Unity often breaks games. It's a common problem for indie developers who have to upgrade every few years since Apple loves breaking old games.

Maybe something like lutris will emerge on Mac.

While there are definitely games that will be lost when deprecating 32bit, I think it's harsh to say that we are going back to the olden days.

If you look at the top sellers on Steam that have Mac support you'll see a very large library of great games that I don't think anyone would have guessed would be supported on Mac 5-10 years ago.

https://store.steampowered.com/macos#p=0&tab=TopSellers

If anything I think Mac support for games is on the rise and will only continue to grow.

How many of them are 64-bit ready? How many that aren't are likely to ever get recompiled for 64-bit? I'd bet that pretty much nothing but games currently getting regular updates are going to make the jump.

Virtually of them are 64-bit ready. In fact they require a 64-bit OS, also on Windows. "Requires a 64-bit processor and operating system"