If you run cat /proc/cmdline in Konsole, do either nomodeset or noveau.modeset=0 appear? If either do, it almost certainly needs to be removed from the kernel cmdline. To test, strike the E key at the Grub menu, then you can backspace it away from the linu… line before proceeding. It can be made permanent via the YaST bootloader module.
More information should help us help you. The X log in /var/log/Xorg.0.log or ~/.local/share/xorg/Xorg.0.log can be uploaded for our inspection either by going to https://susepaste.org/ or https://pastebin.com/ or equivalent in a web browser, or via the cmdline utility susepaste that may already be installed. The inxi information gathering script, if not already installed, either from its author to get the latest inxi version, or from the openSUSE repos to get an antique version, will tell us some detail about your hardware. Please paste inxi output run from Konsole or Xterm or other X terminal here using code tags to maintain its formatting:
What kind of system hardware are you using, recent, old or ancient?
It’s been a long time since even the initial boot(before you log in or the Desktop loads) that 640x480 was the default resolution… For at least 10 years now, GRUB has loaded the VESA driver which usually defaults to 800x600(and supports higher resolutions). Then, after your Desktop loads, a more capable GPU driver is typically loaded but if your problem began much earlier… Who knows what is happening without more info?
Am speculating your hardware needs more specific identification, in particular your GPU card should include model number, not identified as simply “nVidia.”