@zing Thanks for the feedback and sorry if I haven't been comprehensive enough.
This is a new installation on a new rpi 4 with a new sd card and a new hdmi cable.
As for the tests, I replaced the sd card with another card with KODI installed on it and everything works perfectly (with the hdmi cable, vga adapter, ...) I connected my rpi with the recalbox card on my flat screen with the same hdmi cable and everything also works.
There is only on my screen (17 '' 4/3 and vga) of arcade terminal with recalbox that the problem arises.
As for the config.txt file, it does not contain the HDMI lines. I found them in recolbox-user-config but the different modes I configured did not improve.
Is this the correct configuration file?
Any idea where the problem comes from?
Thank you in advance for your help.