[SOLVED] Can't get HDMI 4K on my TV with KDE Plasma & Wayland

[SOLVED] Vizio TV owners: You may need to manually turn on "Full HD Color" to get 4K@60Hz resolutions available! Oddly, this wasn't necessary for X11-based distros tested, but was required for Wayland-based distros tested...

Menu > Input Settings > HDMI-1 > Full UHD Color. It defaults to Off for some reason. 🤦‍♂️

When I was on Debian Bookworm and X11, I could only get 4K video at 30Hz from my GTX 980 Ti. I eventually upgraded from the HDMI cable that came with the 4K Vizio TV to a good brand HDMI 2.1 cable, then both 3840x2160@59.94Hz and 4096x2160@59.94Hz were available and working. (I think 3840 is the TV's native, there were more artifacts on text at 4096.)

I had some issues with Wine games on Debian that I couldn't figure out, and wanted to try some newer/different software, so I went distro-hopping. On both Nobara and currently EndeavourOS, both with KDE and Wayland, I'm back to only having 4K@30Hz available.

Edit: One strange detail I just remembered: Normally, the TV identifies itself as Vizio 55", but when I set 4K@59.94 in Debian, it identified as Vizio 11". Some kind of EDID workaround? I didn't have to do anything special, just install nvidia-driver and replace the cable.

I've only been able to find people with the opposite problem, where they can get 4K on Wayland but not on X11.

Any advice is welcome. Thanks!