Hello Michael, I know what its like to be put through the ringer, when it comes to Linux. As great as Linux is, its not perfect, and driver issues are notorious for making one, want to pull their hair out lol. But I commend you on working your hardest, to find solutions to the problem.
In regards to Nvidia, they like to discontinue driver support, for old hardware. For example, my old 2012 Acer computer is no longer supported, and any new Nvidia driver, will cause the machine to black screen. I forget which Nvidia driver version it can run, but is an old one!
Well, according to Nvidia, the 550 driver is still supposed to support, the 10-series Nvidia GPU's. I just noticed in my additional drivers list, Nvidia 560 is now a thing, but I am still running on 550. But this does suggest that support for 10-series Nvidia GPU's, has now dropped support for driver 560 and up.
Like I said, earlier, this is one of those things, that makes a person want to pull their hair out, cause you don't know if its a Linux thing, or an Nvidia driver thing. This is why some newcomers can't make the switch to Linux, cause their experience doesn't go smoothly.
Part of the issue too, is notebooks with dual GPU's, even though thats been a thing for like 24-years no probably, for some reason, Linux always gets the short end of the stick, when it comes to support for dual GPU's. There is a lot of things that desktop users don't face, that us with notebooks do face, its just the name of the game.
Anyways, back on topic a bit here, it looks like Nvidia 550 is the maximum driver that older notebook can support. And it looks like the larger amount of digging you did, pulled up some issues regards to it. But I do find it interesting that the POP OS repo was able to save you in this regard.
I do know that many drivers can be kernel specific, as I've dealt with kernel specific issues myself. So it might stem around that, as I find it interesting that switching your kernel, suddenly made things working again, and work well. Good advice from @Aravisian as well, about removing the repo once finished.
With all the garbage Microsoft is doing with Windows 11 these days, more people are going to be switching to Linux, with an attempt to make that work for them. So its good to have more then a base knowledge, in order to work through possible problems.
When I switched to Linux, I knew absolutely nothing about it. Linux issues always frustrated me, especially with my lack of developer knowledge. It took a lot of distro hopping, and even Zorin distro versions upgrades, to get where I am today, and I still don't have a developers knowledge lol.
It just shows that Linux can have a steep learning curve, depending on what you are trying to accomplish with a computer. Keep in mind, folks who never game on their computers, or do production workloads, and only use it for general purpose usage, likely won't run into half of what we've had to deal with.
The more of a power user we are, the more we use our computer's for, gaming, production, the more we require of our machines, the more things that can go wrong, either on Linux side, or Nvidia/AMD side. So its a learning process for sure.
I am just fortunate, that Zorin OS 16 is running so good for me as it is. I still remember the OS9 days, when the boot loader cash would get filled up, requiring a manual clearing. It was a problem that would never get fixed until OS12 came out. So, good job @Michel for working through the problem, to find a working solution.