Hi there!
I have recently switched my audio setup from using headphones plugged directly into the monitor headphone jack to a speaker setup which are plugged into the green OUT jack of the motherboard.
However, a strange consequence of this has been that Steam Recording stopped recording audio for specifically TF2. Any other games work just fine, though I have not tested other source games so far.

Plugging in Headphones, or simply plugging the speakers into the Headphone jack at the front of the Desktop PC seems to resolve this issue entirely.

Switching between "Game Audio" and "System Audio" produces inconsistent results. "Game Audio" never records any audio for TF2. "System Audio" seems to sometimes record audio, but if it does, it is desynced from the video footage by a few seconds.

For now, I have plugged in the stereo speakers into the headphone jack of my machine to resolve this issue, but it would naturally be preferable to use the intended motherboard jack for the stereo speakers instead.

Switching between the Steam client beta and non-beta makes no difference. I've updated all my drivers and nothing changes. I am on Windows 10 and am using a Geforce RTX 4070 Ti. Messing around with the Windows Sound Settings does not seem to help - it just boils down to whether or not the headphones are the default device or not.

Thanks.