Comment 2 for bug 1912677

Running two *Ubuntu installs on the same system is not really supported, as there can only be one grub installed.

Same for os-prober really, it doesn't really work correctly for anything other than Windows.

So I understand that there's an issue, and we can fix this, but the expectation is that os-prober will go away at some point, and you should not run two ubuntus on one system.

Though I guess you can override the grub distributor is environment variable to hack around things, making the second Ubuntu install as like ubuntu2 to the ESP, and then select that from the UEFI boot device menu.