Steam Deck HDMI audio does not work with Vizio VA320M TV, but works on everything else (LG/Acer monitors, Sanyo TV, etc.)

Your system information

• Steam client version: 1785187029
• SteamOS version: 3.8.16
• Opted into Steam client beta?: No
• Opted into SteamOS beta?: No
• Have you checked for updates in Settings > System?: Yes

Please describe your issue in as much detail as possible:

I have a 512GB Steam Deck OLED running the stock OS, and an Anker USB-C hub with HDMI. I have used my Steam Deck with this hub over HDMI on my PC monitors and the downstairs Sanyo dumb TV, and everything worked as expected; audio, video—the whole shebang. I recently picked up a used Vizio VA320M TV for the bedroom, and after plugging it into the Steam Deck, I noticed that the video worked just fine, but I wasn't getting any audio from the TV (only out of the Deck's internal speakers). External speakers did not appear as an option in Steam Big Picture mode, and in desktop mode, the Audio Settings page showed Rembrandt High Definition Audio Device as "Off," with no way to turn it on. When the Steam Deck is plugged into my other displays, these settings are populated. The Steam Deck isn't picking up the Vizio TV as an audio device at all.
I've tried power-cycling the TV with HDMI still connected, tried doing the same with the hub powered, rebooted the Steam Deck with the hub both connected and disconnected (and both powered and not powered), and repeatedly reconnected the hub to the Deck, all to no avail.

On my Windows laptop (same-gen AMD APU), HDMI audio on the Vizio works just fine, both through the hub HDMI and the laptop's onboard HDMI port. When I plugged the Steam Deck back into my computer monitor, both video and audio worked as expected.

On the Steam Deck, alsamixer just showed four generic S/PDIF controllers, none of which I had any control over.

This is very frustrating as I'd like to be able to game on the big screen from the comfort of my bed with a wireless controller rather than having to hold the entire Deck.

To rule out a hardware problem/incompatibility, I'm going to try and live boot a different OS on the Steam Deck and see if I have the same issue. I find it extremely odd and frustrating how the Steam Deck works properly on literally EVERY HDMI-capable display I own except for this one.

Steps for reproducing this issue:

1. Plug the HDMI connection of the hub into the Vizio VA320M
2. Plug the Steam Deck into the hub
3. Notice how video works, but not audio.

No repository files or tests are named. Reproduce the setup with the Anker USB-C hub and Vizio VA320M, then inspect the audio devices in SteamOS desktop mode and with alsamixer; done means the TV appears as an external audio device and HDMI sound works without affecting the other tested displays.