Hi @Manners09, welcome to the Sonos Community!
Are you opening the Sonos app after you start playback from the Sonos app? I’ve tested on my system and if I start playback in Spotify then use Direct Connect to select Sonos, I’m able to adjust the volume using the hardware buttons, which was tested on my Galaxy S22. I’d suggest trying again after closing the Sonos app.
For some more information about this feature when using the Sonos app; if you use Android, our internal information suggests hardware buttons can still work for some devices, however this feature isn’t currently available in the new Sonos app and is scheduled for a future release. I’d recommend keeping an eye on our release notes, as it’s likely to be mentioned in there.
Regarding iOS, this feature was removed in July 2023 and wont be coming back as this feature does not meet Apple’s experience guidelines for their developers. You can still use hardware buttons when you are Airplay-ing to Sonos however.
Note that the Android and iOS differences should only apply if you use or open the Sonos app after starting Direct Connect, otherwise it should work.
So this functionality was removed by Sonos when they launched the utterly useless black app. There’s no way around it that I have found. To make matters worse Sonos couldn’t give a toss that they removed a great part of the previous app. How the tech people have kept their jobs is beyond me.