samidon using arch repositories
Do that, and your install will be hosed, NEVER use unsupported repos (posts regarding users ignoring that are automatically deleted). This is not Arch or Arch based, make sure you know what KaOS is:
Nvidia is in the KaOS repos, 3 versions (340xx for 8+ year old cards, 390xx 5+ and latest 450). Installing non-free Nvidia is even fully automated when starting Live mode with the non-free option.
There are a few things you can do, use a chroot (wifi might be hard there too):
Use any Live media (or use an external USB from within another system) to download the correct Nvida drivers from the repo (make sure to read https://kaosx.us/docs/nvidia/), needed are the kernel modules & utils package, since you can't use pacman -S to get both at once. So you will need nvidia-340xx & nvidia-340xx-utils, or any newer combination. Once downloaded in the Live session, copy them over to the installed system (somewhere easy to find like Download folder), then when back in tty
sudo pacman -U both packages to install.
But depending how you installed nvidia so far, you might get file conflicts, so make sure to uninstall all.
In the future, hopefully you will use the KaOS Documentation.