Hi CalumBurns,
First things first, if your HDMI device is not set as the default device, the HDMI output is unavailable.
Here’s how you can set the HDMI device as the Default Device:
Right-click on the volume icon on the task bar.
Select ‘Playback devices’ > in the newly open Playback tab,
simply select Digital Output Device or HDMI.fix HDMI issues playback devices
Select ‘Set Default’ > click OK.
Now, the HDMI sound output is set as default.
Also, make sure that the ‘Show disconnected devices’ option is enabled,
so that your PC can display all the devices connected to it.
Hope these steps help.
Your feedback is very much appreciated.
Thanks and regards,