Sorry to hear about the upgrade problems. I never did finish the Python script - other stuff got in the way.
However, I have seen that same upgrade problem on my X299 with working NVRAM. It may still be related to NVRAM, as I've been clearing mine out now and then so it's possible some key (maybe the same msu-product-url) is meant to be there and I'd earlier cleared it out. But I definitely did not clear NVRAM during the update process itself.
When I upgraded from 11.1 beta 2 to 11.1 RC1, I watched the process. At the first reboot, I had two new EFI entries in OpenCore: "EFI", and "Macintosh HD", with EFI the first and therefore default. This was in addition to my normal NVMe boot entry. EFI and Macintosh HD looked a bit weird, so I tried choosing my normal NVMe boot entry. I thought it was working because I got a "10 minutes remaining" screen, but after that 10 minutes I was still in 11.1 beta 2 - the update had not applied.
I tried rebooting again, and chose EFI. It did nothing - just took me back to OpenCore. Then I tried Macintosh HD. In the verbose boot log I could see it running commands that I remembered seeing during the initial Big Sur install, so that looked promising. But it rebooted quite quickly, and when I was back to OpenCore those extra EFI and Macintosh HD entries were still there. I tried going into my normal entry, and it was still not upgraded. I tried running Macintosh HD a couple more times, no improvement.
Therefore it appears that if the update doesn't apply right the first time, it won't work.
So I booted into the non-updated 11.1 beta 2, and started the update again. This time, after the first reboot, I tried choosing Macintosh HD. Now it ran those update-y commands for a lot longer. It rebooted automatically, and I think at that point the EFi and Macintosh HD entries were gone. Or maybe they were still there and I had to choose Macintosh HD again, I can't remember. But it did eventually work, and I booted into my normal NVMe entry and now had 11.1 RC1 installed.
So, this is what I'd try, if you haven't already:
- In Big Sur, start the 11.1 update.
- At the first reboot, choose "Macintosh HD" entry if you have it - not your normal NVMe entry.
- Take a note of how long it takes - you should see verbose boot log messages for at least a minute or two, and if you can read them they'll talk about moving files or something along those lines.
- If after auto reboot you still have a Macintosh HD entry, choose it again.
- After one or two reboots in total you'd expect the next reboot to only have your normal SSD/NVMe boot entry. If it still says Macintosh HD after two reboots in total, it's likely not working (but still try selecting it one more time)
- When you reach a boot where only your NVMe/SSD entry is listed, choosethat, and you'll get a slow progress bar, possibly with "X minutes remaining", but possibly not (I think mine didn't have it).
- After that you'll be in to the OS, and hopefully on 11.1.
If one of you guys with issues could try that and report back, I'll investigate if necessary. If you try that and you still can't apply the update, then yeah I guess there is still an NVRAM issue. Maybe a new msu-product-url NVRAM key needs to be set, different for each update process.