Look at incus project list
The behavior you’re describing is consistent with your user being a member of the incus group but not the incus-admin group. In this scenario, your user gets access to a per-user project with limited access to the overall system, effectively to prevent an easy privilege escalation.
If that’s the case, you’ll see your user only seeing a user-1000 or similar project whereas doing the same incus project list as root will show you both the default and user-1000 projects.
If you intend for your user to have full Incus access, add them to the incus-admin group, logout and log back in, then check incus project list again, if the default project correctly shows up in there, you can switch to it as your default with incus project switch default.