Executing snapcraft in 26.04 gives:
snapcraft internal error: ValueError("'26.04' is not a valid BuilddBaseAlias")
To fix it, for now switch to the edge channel:
snap refresh --edge snapcraft
It is fixed by feat(ubuntu): mark Questing as stable and make Resolute available (#850) · canonical/craft-providers@714c8dc · GitHub which is currently only in the edge channel.