Hello,
The "base" snap defines over which basic version you want to develop an app. You can install an app that is based in whatever base, the important thing is that you have that app installed in the system. You can have core18, core20, core22 installed. Not a problem.
Additionally Ubuntu core20 will have core20 preinstalled core20 snap, Ubuntu core22 core22 and so on.
Please start from the basics on the Snapcraft website:
https://snapcraft.io/docs/base-snaps
https://forum.snapcraft.io/t/introducing-base-snaps/381
https://snapcraft.io/docs/snapcraft
Mauro
... View more