Hi N R.
Thanks for reporting this issue in Microsoft Community.
In your description, you were playing a game and after switching the audio output device, there was no sound from the new device, only after rebooting.
I noticed that you tried many kinds of attempts, including changing the default device, disabling the device, etc. Thank you for your efforts in resolving this issue, your efforts deserve to be recognized. I do understand the frustration of having to restart the game when you try to change the output device at the moment.
Can I ask if this issue is occurring on a particular game? Or is it occurring on more than one game?
We suspect that this may be related to the volume mixer settings, so please right-click on the speaker icon in the taskbar after changing the output device while playing a game and select Open volume mixer
In Volume mixer, check if the game uses your new device as the output device, if not, please use the new output device as the output device of the game and try again.
In addition, please download the corresponding sound card driver from your device manufacturer's website and install it on your computer to see if the same problem occurs after that.
Meanwhile, some third-party software conflicts may also cause this problem. To troubleshoot this possibility, I recommend trying a clean boot which starts Windows with a minimal set of drivers and startup programs. It can be used to determine whether a background service or program is interfering or causing a problem.
These steps of "clean boot" might look complicated at first glance. However, to avoid any trouble for you, please follow them in order and step-by-step.
Please open just one game in the clean boot and see if the same problem occurs.
Please let me know the results of your test above and I look forward to your reply.
Best regards,
Zev - MSFT | Microsoft Community Support Specialist