Old post, I know. I'm new to your forum, been on other forums for 20 years. Maybe this will help someone.
When LinuxMint dropped KDE, I switched to Debian KDE. I have an older HP HDX18 laptop with Intel Core 2 Duo T9600 CPU and Nvidia GeForce 9600M GT that I use to stream audio and video to a Vizio TV through HDMI in the basement. From there it goes through an amp out to the speakers. I had Debian Buster 10.2 KDE installed and it worked great. Seeing how I can't leave anything alone, always think I can make things "better", I installed Debian Bullseye 11.5 KDE. That's when I lost HDMI sound to the TV. The laptop speakers worked fine. Since I hadn't touched the HDMI cable or TV, I assumed they weren't the problem. I booted into Windows and confirmed that the HDMI sound still worked. I spent too much time reading about people having the same problem and not finding a solution. Found some advice about installing nvidia-detect. When I ran that, it came back with a message to the effect that my Nvidia GeForce 9600M is not supported in Bullseye, support ended with Buster. Not what I wanted to hear, so I gave up on Bullseye. There's probably a solution, but this is just a multimedia setup and I don't use it for anything else. I downloaded Debian KDE 10.13 after reading this:
https://www.debian.org/News/2022/20220910 I followed the instructions for installing drivers from this page:
https://phoenixnap.com/kb/nvidia-drivers-debian I used the first method on the page, installing drivers from Debian repository. Nvidia-detect said that my 9600M was only suppported up to a legacy-304 driver, so I installed that. Towards the end of the installation I got a warning that popped up that is not mentioned on the instruction page. It said something about the nouveau driver is interfering with the new driver and the best way to fix it is to reboot. Maybe all systems don't get the warning window, and the reboot step is further down the installation instructions. Just click OK and the installation finishes. Reboot. Now when I go to System Settings>Audio Volume>Advanced I have the option in "Profile" of Digital Stereo (HDMI) Output. Now the sound is playing through the TV and not the laptop speakers, which is all I need.
Shark