After a lot of fiddling I’ve finally gotten my TV to display 4K 120Hz, after I discovered HDMI 2.1 is not a thing in linux.
Now I have a second problem. The sound is not routed through the displayport output. Technically everything works, drivers are loaded and working, but there’s no sound received, which makes me suspect the sound is still routed to the physical HDMI port.
Any tips? (And yes, it works it windows).
Welcome to the community @Trym 
It’s a real shame about HDMI Forum’s closed spec on HDMI 2.1, conflicting with the open-source nature of Intel and AMD Linux drivers.
Could you share some specs, that will give a better picture of options you might have available to you.
inxi -SMGAx --za
Your TV brand and model would help as well.
With respect to using a DisplayPort > HDMI conversion, that can be dicey territory. I’d personally be attempting that with a single DisplayPort > HDMI 2.1 cable (not adaptor) that clearly specifies audio support, validated by reviews/comments.
If you look at this cable for example, it states audio support, but comments indicate issues there, so perhaps not that one.
Sure!
System:
Kernel: 6.13.2-arch1-1 arch: x86_64 bits: 64 compiler: gcc v: 14.2.1
Desktop: KDE Plasma v: 6.3.0 Distro: EndeavourOS base: Arch Linux
Machine:
Type: Desktop System: ASUS product: N/A v: N/A serial: <superuser required>
Mobo: ASUSTeK model: CROSSHAIR VI HERO v: Rev 1.xx
serial: <superuser required> UEFI: American Megatrends v: 8801
date: 08/30/2024
Graphics:
Device-1: Intel Battlemage G21 [Arc B580] vendor: ASRock driver: xe
v: kernel arch: Xe2 bus-ID: 0b:00.0
Display: wayland server: X.org v: 1.21.1.15 with: Xwayland v: 24.1.5
compositor: kwin_wayland driver: X: loaded: modesetting dri: iris gpu: xe
resolution: 3840x2160~120Hz
API: EGL v: 1.5 drivers: iris,swrast platforms:
active: gbm,wayland,x11,surfaceless,device inactive: N/A
API: OpenGL v: 4.6 compat-v: 4.5 vendor: intel mesa v: 25.1.0-devel
glx-v: 1.4 direct-render: yes renderer: Mesa Intel Graphics (BMG G21)
API: Vulkan v: 1.4.303 drivers: N/A surfaces: xcb,xlib,wayland devices: 2
Info: Tools: api: clinfo, eglinfo, glxinfo, vulkaninfo
de: kscreen-console,kscreen-doctor wl: wayland-info,wlr-randr
x11: xdpyinfo, xprop, xrandr
Audio:
Device-1: Intel vendor: ASRock driver: snd_hda_intel v: kernel
bus-ID: 0c:00.0
Device-2: Advanced Micro Devices [AMD] Starship/Matisse HD Audio
vendor: ASUSTeK driver: snd_hda_intel v: kernel bus-ID: 10:00.4
API: ALSA v: k6.13.2-arch1-1 status: kernel-api
Server-1: PipeWire v: 1.2.7 status: active
It’s a TCL TV from 2020, 2xHDMI 2.1 ports, 2x1.4 ports.
I’ve tried with another known good cable as well, same thing.
And again, the exact same hardware config works in windows, sound comes over the adapter no problem.
Thanks for responding. Let me know if you need any other logs.
So, after trying disabling all the unused ouput ports (video=HDMI-A-3:d and so on), which didn’t work, I simply moved the adapter from the recommended DP-1 port, to another DP port, DP-2 in this case, and voila, it works! 4K 120hz with sound!
[EDIT]
That was not the solution. This is:
What I didn’t mention is that when my TV does not pick up the 120hz signal, I have to do ctrl-alt-f2 and ctl-alt-f1 a few times to get TV to pick up the signal. (I have no idea why windows does not have this problem). THAT is what destroys the audio. So the solution to this again is to put the computer to sleep, wake it up again, and this fixes the audio. I’ve tried just restarting the audio-components, and that does NOT work.
This is probably some kind of bug (that audio is not restored upon ctrl-alt-f1).
Thanks for sharing the fix @Trym, I wouldn’t have guessed. Something to keep in mind 
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