When pressing the volume buttons on the Quest headset does nothing. This feature works without FMOD in Unreal 4.27, however doesn’t work with FMOD in 4.26 nor 4.27. The volume control was working on 4.24. I’m using FMOD Studio 2.02.03. I understand if this is hard to debug, but I’m happy to assist with anything.
Apologies for the delay, this is indeed a hard one to test. Going through the OVR plugin it looks like system volume is no longer accessible and you need to handle it yourself with the Optional Mobile Features Blueprint Library Plugin. Once that plugin is enabled, you should then have access to Get Volume State, and can set FMOD’s volume manually with Bus Set Volume or VCA Set Volume.
Can you please try that and see if it that works for you?