Fenix 6 pro: I can not activate my own programmed watch face

I had a Fenix 5x in the past. I have programmed my own watch face. I compile that for device (release) and copy it into the 'NewFiles' folder. On the Fenix 5x I can activate that watch face.

When I do the same thing on my new Fenix 6 pro, it is not possible to select my watch face. It does not appear to select it as the new watch face.

Any clue what could be the issue or what I'm doing wrong?
(When I copy a segment to the device, that is properly shown)