I believe so, yes. Other than that there's the official closed driver. Nvidia also "open-sourced" their driver for the RTX 20 series and up, which you could technically run, but I didn't hear much good from it.
And the parts that are open source are basically just a code dump. No commit history, so no comments explaining things in commits. That's worse than some source code leaks.
Some people might have gotten their computers before using Linux, and the GPUs are either too hard to swap (in some prebuilts and most laptops), or new ones are too expensive.
That's the situation I'm in. 12 year old me did not know the problems Nvidia had with Linux, especially Wayland. My server on Ubuntu did not have problems with the GT 210 after all - which was to be expected considering it was headless and just used Nouveau.
For it to be very hard if not impossible to swap in Laptops I agree, that's true. For desktops it should be a drop-in replacement tho, considering the equivalents of AMD to Nvidia all need the same, if not less, requirements (Power, Other components, Plugs). Selling my 1070 I would get ~100€, which is the price of a used RX Vega 56, the AMD equivalent of my card. Considering I want to upgrade in the near future that would be pretty pointless however.
No. Since Nvidia began partially opening up their drivers a new open source alternative has been in development based on that info. He's resigning because he thinks the community should focus on that driver instead now.
NVIDIA creating an open source driver (well, throwing code over the wall once in a while is still open source I guess) does not mean there's an upstream driver. The kernel maintainers have already noted that it's definitely not in any shape to be merged upstream (and would need close to a full rewrite)
"He's resigning because he thinks the community should focus on that driver instead now" is completely false and I have no idea how you even got to that conclusion. Literally on the same day he posted this email, he also posted initial GSP support which specifically gives us a bright future in nouveau, as it means we can now do funky stuff like reclocking (and which will be further developed by some other people in his team at RH).