I have had many issues in upgrading online from leap 15.6 to leap 16.0 and tumbleweed. My system has become convoluted over the decades because of many apps I have compiled outside of Yast/zypper/rpm and the upgrade does not know they exist. I am trying to save them.
I have upgraded many times and found issues that I did not have the time to address. Through use of the “timeshift” app, I have been able to revert back to my initial OS state successfully on about a half a dozen times.
I simply do a “timeshift” rsync snapshot prior to each upgrade test and use that to revert back to. I would recommend that others doing the online update do this so they can get back to where they were should the need arise.
I do not have btrfs file system. It is ext4. I use x11 and nvidia proprietary graphics drivers. In several upgrades, I lost graphics and I was able to revert back using “timeshift” from a text login, i.e., w/o graphics. “timeshift” does 1.2 million commandline actions to make the restore and it takes a couple of hours . But, it has always worked.
There may be other apps that can do the same but “timeshift” has been working flawlessly for me. I am not affiliated with “timeshift” in any way. I just wanted everyone to know it works and should give you confidence that you can get back to where you were should you encounter an upgrade issue.
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thanks, tom kosvic
and as the Maintainer of timeshift, your welcome 