Please correct anything I am misunderstanding. Reading your posts above, it looked like you went from 15 to 16, but were on 16 for a time without trouble.
You then noticed that Flatpak Installed some drivers - But I am not aware of Flatpak ever handling Nvidia drivers, due to the absolute necessity for System Handling of those drivers. Flatpak is containerized.
You can double check with
flatpak list
I recommend Purging all Nvidia drivers first and then immediately run
sudo ubuntu-drivers install
Do not reboot, log out or shut down in between.
After running the above install, then open Software & Updates > Additional Drivers and try the 470 (Proprietary) driver. I suggest not trying to use "server" or "open" or the 470 (Proprietary Tested).
Just 470 (Proprietary).