I have this issue too, on Quest 3 tho.
No fix yet but my current workaround is to quickly open the Quest home, adjust the volume, then resume back to SteamVR. maybe reinstalling SteamVR may help, idk.

i'm also having the same issue, the only solution i've found online is that people have a keymapper that seems to be installed with sidequest and that's messing with the volume buttons, although this doesn't help my situation because i don't use sidequest or have a keymapper. I hope someone finds the reason this is happening

I've found the issue, there is a bug in the current public stable build of steam link, so opting into the beta or rolling back a version should fix the issue.

you can change what build of the app you are on by going to your apps in your quest menu, clicking the three dots that appear when you hover over the steamlink app and going to settings, once you are in the settings page there should be a "release channels" drop-down menu next to the "installed version information". Clicking on this brings up a menu of different versions to pick, you'll want the public beta option (or previous if you want a more stable build). Once it's selected the app should automatically update and you're good to go !