Ohh yeah, i remember i had this problem also after my change from x11 to Wayland on my AMD Laptop.
It reverted after a reboot again, but this way you can make it permanent:
System Settings>Colors & Themes>Login Screen (SDDM)>(The button at the top)Behavior>select Automatically Log in “USER” with session “Plasma X11” or “Plasma Wayland”.