Well, I would love to say the move to 0.6.6 was seamless and perfect.....but I can't.
For me, it was very difficult. My main macOS load is Catalina. But I do load Big Sur on an internal SSD (as I use it primarily as a test system and don't intend to move to Big Sur until I'm fully confident it's reliable and ready to use for my production needs).
I downloaded your posted config for 0.6.6, and did what I usually do. Adapted the config to my needs. In the past, this has worked perfectly, but not this time.
The first problem was that OpenCanopy would not load. NVRAM clear didn't help. I thought I had missed something, so I started adjusting the config to more conform to your basic config. Still couldn't get OpenCanopy to load.
Finally, I had to load your config, with no modifications whatsoever and add my needed configuration changes one by one (NVRAM is a perfect example, but there are others). So, after doing that, and another NVRAM clear, OpenCanopy was loading.
But then I noticed another problem. My OWC TB 10G adapter was not connecting - at all. I tried a number of things, but finally I just went in to /Library/Preferences/SystemConfiguration and deleted all configs related to networking.
I rebooted and cleared NVRAM, and it started to work. Then I loaded the debug version of 0.6.6 (which I prefer to load) and very carefully added in my config preferences.
Some 2 hours later, I was up, or so I thought.
On my Big Sur beta, I swapped the EFI and the /Library/Preferences/SystemConfiguration config data, rebooted and it started just fine. No issues with the TB 10G adapter or anything else. Cool....
Now, I moved to my backup disk for Catalina (which I boot from a TB port or a USB port, depending on what I'm doing with the system), and I did the same thing I did for my Big Sur beta install. Rebooted and got a KP (yes I saved the notice, but it listed IONetworking as the issue). Several boots later, still getting KPs. Okay, so now I booted into Catalina and did a CCC overwrite, cleared NVRAM and rebooted. Got it now I thought, but no, another KP. Then I wiped the backup disk entirely, recreated the EFI partition, added my now working EFI from my main boot disk, and did a complete restore to a now empty partition on my backup disk.
Once again, after the complete restore was done, I rebooted, cleared NVRAM, and finally, now after 3 hours, my backup disk was working again.
Just thought you'd like to know what my experience was in case someone else hits a similar speed bump....