"The multipass launch command without any argument will create and start a new instance"
Not clear to me what is actually happening with this. Is it running Ubuntu on another computer, x11/ssh/rlogin/etc ? Or does it create a local virtual machine?
Is the instance persistent, or does it (and all its data & history) cease to exist when you're done with it?
If remote and persistent, does it make you the only user, or might there be other login accounts on it?