Apple locks old devices out of updates, although it takes about 10 years to do so. And after that, you can still do a workaround. Only problems is going to be when the last intel mac isn’t going to be supported anymore, then the old devices will definitely be locked out.

You can search on e.g. Lutris if the game is supported. It’s usually just a one button install

Install linux :)

What’s the point of open sourcing this product?

Some people just like to have the possibility to change and completely own their stuff. Some people actually do change firmware or hardware components. I’d say it’s mostly for tech enthusiasts and tinkerers.