Use Windows 10 PC (Version 10.0.19041 Build 19041) and a pair of HC Gamerlife Headphones (ASIN: B07BHYZFLF).

They have been working fine, but recently (within the last day or so) any audio I play on the computer comes out through both the headphones and the computer's internal speakers.

I have tried:

1. Checking for driver updates.
2. Opening "Playback Devices" and setting the headset as the default device.
3. Hardware and Sound > HD Audio Manager and tweaking relevant settings.

None of these have worked. I also tried a simple restart to see what would happen but to no avail. Any ideas what to do?