You shouldn't have to install any flatpak dependency manually. Flatpak should handle it for you automatically when you install your programs. (In most cases.)
Not sure if it detects the presence of an NVIDIA driver on the system though. Flatpak is normally separated.
Those Flatpak drivers for your Nvidia card will be installed if an application depends on it. I think you don't need to install them yourself. And over time you might end up having multiple versions of the Nvidia driver installed as Flatpak, just because each of the applications depend on a specific driver version. This was my experience until last year on my main PC, with the proprietary driver using a GTX 1070.
To uninstall all unused Flatpak packages, use the command: flatpak uninstall --unused (but I think this does not work for the Nvidia drivers for unknown reasons to me)
How would Flatpak know which driver to install?
I think its a dependency of the application you install, that makes use of the driver. The programs don't use your native graphics driver, but a version from Flatpak. I suppose the packager can specify dependencies, just like KDE software would install the entire KDE suite as dependency.
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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
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