There is a way to get HDMI 2.1 support in Linux, but it's an adaptor hack that isn't perfect.
With Linux lacking HDMI 2.1 support, getting your games onto a 4K TV over HDMI can be troublesome.
Playstation 3 and Playstation TV capture or upscale with a RetroTINK 4k.
After connecting my MiSTer to my TV setup, all my HDMI devices stopped working together. Here's how to fix.