Thanks for your answer.
SD card is brand new, no error on basic checks. Do you have a specific tool/check you want me to perform ?
According to this post YunoHost 4.0 (Buster) release / Sortie de YunoHost 4.0 (Buster) , the raspberry image is not ready yet.
And the previous one is not available anymore (dead link). At this moment, there are NO valid, working raspberry image. Could somebody please make the previous image available again ? (this file yunohost-stretch-latest-rpi-stable.zip)