MacBook Pro suddenly not connecting to HDMI
In System Preferences > Displays > Arrangement > turn Mirroring on or off, whichever it wasn't set at.

Then resetting the NVRAM again https://support.apple.com/en-us/HT204063

and the last opportunity is to change the Mirroring back to what is was before and reset after that the NVRAM again.

I hope I could help you..