I've now updated to v2307 from https://rog.asus.com/forum/showthread.php?118522-DRIVERS-Realtek-USB-Audio-(MB-Intel-5xx-6xx-amp-AMD..., to no improvement (over v2306).
Note that the test shown in my most recent video does not reproduce on Chrome, only on Firefox. On the whole, the new firmware version (and perhaps driver) seems to have reduced the occurrences of the issue, it still persists in some cases. Notably, my previous repro steps against the sound control panel test all seem to pass now, and I have only noticed the issue a single time with the real Discord notification in the last day.
Thank you for that update. At the very least it's no longer as glaring a fault as it previously was.
However, "rarely occurring" isn't quite good enough for my purposes, so for the time being, I will go back to using the stereo mix workaround.
Did you also upgrade the firmware?
May I double confirm only when you open firefox in background, the notifications(discord, MS Teams, Element/Matrix) sound would be cut off?
Could you please install the Realtek USB Audio Driver V6.3.9600.2307 from our support site with bios all default settings to check the discord and the notifications (MS Teams, Element/Matrix) you mentioned in firefox?
Tried the linked drivers, no detectable improvement over my last test.
Hope you got more luck than I did thus far, at least the static audio bug seems gone for now. Now if we can fix this wake up delay were getting somewhere.
Just like OP, the same issue still occurs on the z590 platform (makes sense as its the same audio chip and even the same drivers.)