Setting screen size after intalling LEAP 15.3

You do have drivers from the repo, but somehow installation went wrong it looks.

I would first remove existing drivers


rpm -e nvidia-glG04-390.147-lp153.11.1.x86_64 nvidia-computeG04-390.147-lp153.11.1.x86_64 x11-video-nvidiaG04-390.147-lp153.11.1.x86_64 nvidia-gfxG04-kmp-default-390.147_k5.3.18_57-lp153.11.1.x86_64
mkinitrd

reboot and try

zypper install-new-recommends

this should suggest the same drivers. It may suggest additional packages depending on whether you disabled recommended packages by default.