Hello PG,
Your tests strongly suggest that KB5124008 triggers a compatibility issue with the headset’s USB 7.1 mode. A 3.5 mm cable carries stereo, so it would not restore that functionality.
If disabling audio enhancements does not help, the most reliable temporary workaround is to uninstall KB5124008 again, since you have already confirmed that removing it restores sound.
Go to Settings > Windows Update > Update history > Uninstall updates, remove KB5124008, then restart. Instructions: https://support.microsoft.com/en-us/windows/deployment/updates-lifecycle/how-to-uninstall-a-windows-update
You can briefly pause updates to prevent immediate reinstallation—for example, seven days: https://support.microsoft.com/en-us/windows/deployment/updates-lifecycle/pause-updates-in-windows
This temporarily removes the update’s security fixes. I cannot currently confirm a solution that retains both this update and working USB 7.1 audio.
Please also report the issue through Win + F, including that 2-channel works, 7.1 freezes audio, and uninstalling KB5124008 restores operation.