
Maybe I shouldn't hijack this thread but I have struggled with this problem and given up so didn't want to trouble people with a new post.
Question: if I want to try "The Hard Way", is the driver I want the one listed here
https://opensuse.pkgs.org/15.3/nvidia-x86_64/
as "NVIDIA graphics driver for GeForce 600 series and newer". It is available at
https://download.nvidia.com/opensuse/leap/15.3/x86_64/
Is the only other package I might need the "NVIDIA OpenGL libraries for OpenGL acceleration"? I admit to being ignorant of the function of all the files available at these sites.
I have purged every reference that I can find to Nvidia from my installation of 15.3 as I was going to soldier on with the nouveau driver which is almost usable some of the time and look towards replacing my graphics card, so was not keen to try the "easy way" again.
If anyone is interested my saga went as follows
*Identified my Graphics card as "Nvidia G86 [GeForce 8500 GT] (rev a1)"
*Downloaded driver NVIDIA-Linux-x86_64-340.108.run as the correct one to install the "Hard Way" (I thought it might work better than the GEforce 600 series and newer as the "Right" one!

*when this failed I tried the --use-this-kernel option; the interface was the first thing it tried to do and it failed.
*Installed the GeForce 600 driver the easy way; this succeeded but the only resolution available was less than that recommended for my monitor so the right margin of the screen was cut off. It seemed stable through reboots. I did various things like run nvidia-xconfig and reboot into a previous snapshot to compare the functionality. I shut down as there was a thunderstorm.
*when I rebooted, I had a lovely desktop! Perhaps I should have made a snapshot or done a mkinitrd but I thought my torubles were over. There was thunder on the left (Superstition!) so I shut down again to save all my hard work.

*Booting up the next day, no graphics

only a login prompt!
Thinking this through, maybe I should just try the easy way..
Any advice gratefully accepted, and again apologies for adding all this to this thread which seems to be solved.