Setting the variable LANGUAGE is effective to modify the date property’s format in reading view on Fedora 40 running under GNOME. The only two options that I found to order the date as YYYY MM DD are JA and KO. KO is Korea with this format YYYY. MM. DD and JA is Japan as YYYY/MM/DD.
I have this line for exec in my obsdian .desktop file.
Exec=env LANGUAGE=KO obsidian %U