I noticed with Pinephone Keyboard that the best order use HDMI is:
1. Start Pinephone Keyboard.
2. Connect HDMI cable to Docking Bar.
3. Push two times charge button (right side of keyboard) to stop use secondary battery
4. Connect Docking Bar to Pinephone side USB port.
5. Use xrandr command

If xrandr say resolution not supported check that TV or monitor does not sleep.