Firstly, thank for this kit - it serves me very well as a bastion gateway. But given that it's a single point of failure, I don't want to upgrade it if there's the chance of it failing.

At the moment, I'm on Bionic ( but want to upgrade to Focal.

Some questions:

1) Is there a way to do a quick backup of all files that have been altered in the overlay FS that can be used as way of restoring in case of problem?
2) I notice that whilst it's possible to do a readonly remount of mmcblk0p1, it's not possible to mount mmcblk0p2, and also the overlay work and upper directories (/data/...) are not visible. So how do I backup mmcblk0p2?
3) What is the upgrade method to upgrade the kernel, and root filesystem from Bionic to Focal?
4) ... and is there a safe backout method?

Best Regards,