You don’t need to use both of the Sony WF-1000XM5 earphones at the same time. To see how you can utilize only the left or right ear bud of this wireless headset, you can take a look at this tutorial from Seeking Tech.
To only use one of the earphones, you can simply wear one on your left ear or right ear. You can leave the other one inside the carrying case as it should remain disconnected and turned off.
After wearing one of the earphones, any stereo audio will automatically be mixed together for mono playback.
It is important to note that the music playback touch controls are assigned to the right earbud. So, if possible, we recommend wearing the right earpiece for music listening.
If you prefer only wearing the left earpiece, then you have to use the controls of the connected device (such as smartphone) in order to control the music playback. You can also use the “Sony | Headphones Connect” app of your phone to change the touch control functions of the Sony WF-1000XM5 left earbud.
To find out more about the touch controls for both earpieces, you can take a look at this tutorial.
If you want to use both ear buds at the same time, then you need to take the remaining earphone out of the charging case and then wear it.