Single-sided deafness

Operating systems often come with all kind of accessibility options.
If you have a strong imbalance, you might compensate using the balance of your source.
If you are deaf at one side, you might set the audio to mono.

Android

Got to the Accessibility section in the settings.

 

Open Hearing enhancements

Plug in your headphones to activate the "balance" option.

Windows

Open Settings and choose Ease of Access (or simply type mono in the search box).

In the side bar, select Audio and activate mono.

 

Balance can be find in the audio panel of the specific device.

Balance is applied first so if you lower the L to zero, you remove the L channel completely.

If you then choose mono, you only get the R channel.

You can't sum to mono and move this mono signal to one ear only.

Bluetooth

A Bluetooth headphone might offer the option to mix stereo into mono.

Makes you completely independent of the source.

Avantree Aria 8090T with built-in stereo to mono mixer