To force the output resolution of the Zappiti 4K HDR, you can try this:
1. Switch on your Zappiti
2. Click on Settings.
3. Click on Developer options
4. Click the option "Ignoring HDMI EDID"
Note: This option is named "YST Mode" in old firmwares.
5. Return back to the general settings by pressing "BACK" button of your RC.
6. Go to Display.
You'll be abble to force a resolution. Press DOWN to scroll the page.
In fact, Zappiti may fails to render the video giving you a black rectangle instead (or grey if HDR video). If you experience this issue, please do not use the "Ignoring HDMI EDID" option or go back to 3.07 firmware.