Thank you very much for helping me.
I didn't make a normal user account (so only root) and that's why no /etc/sysconfig/desktop file was made.
So I made one myself.
I have to add that there's also /etc/X11/prefdm which is just a simple script pointing to that desktop file you and I mentioned above.
I think it's executed before /etc/X11/xinit/Xclients but since both point to the same file it doesn't matter.