I have successfully verified ubuntu-release-upgrader 1:19.04.16.8 on a disco multipass instance. Enabled disco-proposed, upgraded all the packages (the upgrade also pulled in a new kernel from -proposed), ran do-release-upgrade and confirmed that a reboot is required. And after rebooting the upgrader worked as expected.
I have successfully verified ubuntu- release- upgrader 1:19.04.16.8 on a disco multipass instance. Enabled disco-proposed, upgraded all the packages (the upgrade also pulled in a new kernel from -proposed), ran do-release-upgrade and confirmed that a reboot is required. And after rebooting the upgrader worked as expected.