Until just a few months ago, a Mac was good for work and little else. You could play on an iMac or a MacBook, of course, but not very graphics-intensive games. Things began to change with the entry of the Apple Arcade gaming platform.
They are games developed for macOS Catalina, already with a certain quality. but the qualitative leap has been made by the new streaming gaming platforms: Nvidia Geforce Now and Google Stadia. A new system to play taking advantage of current ultra-fast internet connections. The game is processed on the platform's server, and your Mac simply acts as a screen and as a controller. Simply Brutal. Now Google Stadia already streams to your Mac in 4K. Almost nothing.
Google Stadia just received a small update to its streaming system, surpassing its direct rival Nvidia GeForce Now in image quality. From now on, you can get the game image in 4K (UltraHD).
Requirements
This improvement in video quality simply requires three things from the user. The first, obviously, that your Mac has a 4K screen or higher, the second, having a fast internet connection, and the third, having Google Chrome installed.
If you have these three things, once inside the game, press Shift + Tab and you can choose the 4K connection.
4K, but few games
Google Stadia generated a lot of buzz at first, but its users are a bit disappointed. Its catalog of games is small and expanding very slowly. The problem is that the games have to be reprogrammed again to be compatible with Google's servers. On the other hand, this does not happen with the GeForce Now platform, with more than 1.000 video games in its catalog.
Google has more news for Stadia in mind. A free basic subscription level and the addition of YouTube will come, among other improvements yet to be revealed.
I think you have forgotten the most important requirement, to have a gpu with VP9 hardware decoding. Without this 4k will not be possible, because the cpu will not give and will introduce a latency in the decoding.