That generation card relies on proprietary driver and kernel modules.
You can hound official devs to release the source so us folk can tweak and compile it ourselves as is possible with the open drivers for newer cards, but don’t hold your breath waiting.
For now, you’re stuck using the [nvidia-390xx-dkms]( AUR (en) - nvidia-390xx-utils ) package from the AUR or the open Nouveau package.
v390 has been unmaintained for ages, so surely has a lot of security issues… Nouveau (which is included by default in most distros) is IMO currently the only sane option.
Sorry to be the bearer of bad news but with NVIDIA hardware that old, you’re going to be better off looking at using an older LTS distribution and running with that until it’s EOL.
If you go with proprietary drivers, you probably won’t be able to use them with Ubuntu 26.04 LTS as Canonical already dropped support for GNOME Xorg sessions in the release prior. You would definitely want to use Xorg with drivers that old, as NVIDIA hadn’t yet added GBM support to the drivers at that time.
If you were to use Wayland to get yourself on that version, you’d be stuck with EGLStreams, which is not only poorly supported with modern Wayland compositors, but now has no backwards compatibility for X11-native software either, meaning no old Linux-native video games and problems running any Windows-native software with older Proton/Wine versions too.
Modern web browsing will also suck without X11 as you’d need a VDPAU→VAAPI conversion library to accelerate video decoding, which won’t work under Wayland either.