Stii can't upgrade one of my systems to 21.04

[Grizzly]

22 May 2021  at 16:08, Chris Green wrote:
Stii can't upgrade one of my system (at least in part)

>It would appear that the bug that delayed ubuntu 21.04's full release
>has now been fixed, but I *still* can't upgrade one of my systems, it
>keeps saying "No new release found.".

>My other system upgraded OK a few days ago using "do-release-upgrade"
>so 21.04 is available/released.

>How do I get my recalcitrant 20.10 system to upgrade?

I "think" that do-release-upgrade only offers after the firsdt point release 
(or is that just on LTS releases?)