@zing
Thanks for the answer.
I will try this. As the Pi400 is the plateform i built the Image on, from scratch, so it was clean, and i never touch any of the custom setup except the theme and PPSSP for graphic optimization.
But after finalizing my setup at the bar, on a Pi4, then when back home the image did not start on Pi400 anymore. Still works fine on Pi4.
I had to switch the HDMI though.
I burnt it again, and same result.
I will try the factory reset, but i feel something is odd. I also had the same problem with another image based on a clean 7.2.2 made for my arcade cabinet.
I could not make it boot on a Pi400, even if it was started on this machine...
I never had this problem before on my Pi400 with 7.1.1 or 7.2.1.
Another problem i saw as well, is that when i switch to another Pi4, sometimes the Recalbox reset my setup ( like themes, hidden games, or Virtual menus )