You need to first calibrate the esc .
You can do it connecting the Esc directly to the radio receiver or with to Pixracer via the Mission Planner utility.
If you go for Mission Planner calibration first calibrate the radio of course.
As it turned out the Safety Switch feature was enabled, and I do not use a physical switch. When I disabled the feature the ESC came alive.
Interestingly, the safety switch settings do not get recorded when you save an arduplane configuration. In any new setup they come up set to enabled - I suppose that is for safety and that’s a good thing.