You won't be able to perform BRAVIA Sync (HDMI-CEC) operations when video from a connected HDMI device is displayed using the Picture-in-picture (PIP) feature. This is an Android™ 8.0 specification.
Exit the PIP to use the BRAVIA Sync functions:
- On the supplited TV remote control, press the HOME button.
- Select Full screen.
CEC: Abbreviation for Consumer Electronics Control