Just to make sure things will go smoothly: Will upgrading from 18.04 LTS to Ubuntu LTS 20.04 break my LXD 4.0?
Obviously, the upgrade between the LTS versions should not break your LXD. If it does, then it is a bug.
Are you able to take a backup of your LXD installation as a precaution?
When upgrading an operating system, the standard process is to always backup for any eventuality.
Obviously, just wanted to get some reassurances. Better to be safe than sorry. And of course I would utilize the snapshot functionality of my VM provider.
The snap shouldn’t change at all, neither should the version of snapd, so it’s just the rest of your system changing around it which should be pretty painless.