When Enhanced Headphone Mode (EHM) is on, Audio Output settings are automatically set to "Headphones."

If you change the Audio Output to anything other than Headphones while EHM is on, it will turn off EHM. This is not recommended.

To use EHM correctly, keep your Audio Output set to Headphones while EHM is on.

When in doubt, turn EHM off and back on, then check that Audio Output is set to Headphones. This confirms Enhanced Headphone Mode is active.