[...]I wanted to test against the proprietary driver...
The driver, has nothing to do with the hardware coding and decoding on this very old machine with a very old video card, with 256 MB of DDR 2. This capabilities, are available only for high-end video cards, with at least 2 GB of DDR. In fact, you need at least 4 GB (4096 MB!) of GDDR in order to be able to process hardware coding and decoding. The cheapest solution is NVidia Quadro K2000 with 4 GB GDDR. So, even if you install "the latest & the greatest", driver it will do nothing; simply because you need another laptop with another video card to do such things. I have a GeGorce GT107 (GeForce GT630 OEM) with 2 GB DDR 3 and does nothing as such. The GPU, lacks the capabilities to use the NV_ENC driver.
So, the driver is OK. The hardware is the problem.
Think of this: you are running an 2022 OS, on a 2007 machine, and IT DOES WORK!
Try to install Windows 11 on the same machine. See what you get...
Anyway, Linux Lite 6.x, does wonders on very old machines. See the video below:
https://www.youtube.com/watch?v=NypE2bMd53Y
Best thoughts! :)