I tried several clean installations of EoS (xfce-vanilla option) and every time I rebooted I had the EoS Atlantis wallpaper as my desktop wallpaper.
now after finishing my tests and decided to install permanently EoS (xfce-vanilla option) and after the restart I find the desktop of xfce and no longer that of Eos Antilatis
is this normal or have I broken the installation of EoS?
Hmm…not sure been a while since I installed XFCE. Regardless if you want the EndeavourOS theming you can add it via the welcome app as well as additional wallpapers.
I forget which is which but between offline installs and online installs of XFCE one has theming and one is vanilla (plain). It sounds like you did two different installs one online and one offline. So if one had the theming as well as the wallpaper and the other has neither this is a possibility. If the exact same thing was done twice you should have gotten the same result.