Hello everyone,
Upgrading from distro isn't supported officially but I tried it anyways and thought I should share my findings. In short, it worked for me. Others have reported issues so maybe we can figure out what causes these issues.
My N2+ is fairly vanilla, so I didn't heavily modify it.
Running 5.10.x kernel since that is recommended for de N2+
Step 1. Fully upgrade your system on Focal
sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade
Step 2. Shutdown you N2+ and make an image backup of your emmc using dd or Win32DiskImager in case something goes wrong
Step 3. Boot up your N2+ again, disable all 3rd-party applications and PPA and change the release your sources list.
sudo sed -i s/deb/#deb/ /etc/apt/sources.list.d/*.list
sudo sed -i s/focal/jammy/ /etc/apt/sources.list
Step 4. Update sources
sudo apt-get update
Step 5. This is were the tricky part starts, upgrading packages. Apt will ask to automatically restart services, allow this. Apt will also ask to replace configuration files, personally I kept all my configurations after manually checking them.
sudo apt-get upgrade
sudo apt-get dist-upgrade
Step 6. Reboot the device
And if everything works fine
Step 7. Re-enable 3rd party applications and PPA and change the release
sudo sed -i s/#deb/deb/ /etc/apt/sources.list.d/*.list
sudo sed -i s/focal/jammy/ /etc/apt/sources.list.d/*.list
sudo apt-get update
sudo apt-get dist-upgrade
Step 8. Do a last reboot and done, you should be on Jammy.
Remember manually upgrading like this is not officially supported by armbian!