I want to upgrade rom 20.04.3 LTS To 21.04.
The Software Updater shows that the software on this computer is up to date, and
"However, Ubuntu 21.04 is now available (you have 20.04)"
Pressing the "Upgrade" button simply results in the dialog box to close. Nothing else.
BTW, I am prepared to do this via 20.10 if indicated.
Have you tried ignoring the Software Updater and downloading 21.04 directly from the Ubuntu web-site, then creating a bootable installation usb drive, then (WARNING WARNING WARNING this will completely erase your 20.04 Ubuntu partition with all your data - back up all your data first) install 21.04, and finally reinstall all your applications?
Admittedly, having the Software Updater actually work would be a way-better solution.
You would be better off, if you start from scratch and install UM 21.04 directly. However, since 21.10 is not that far, I would recommend to wait until October. UM21.04 is only supported until January, and you would be forced to upgrade again to 21.10.
Upgrading to a newer version wipes out the programs and since you have to reinstall them, it's better to start from scratch.
First - backup anything you want to keep
Have you tried menu > administration > software & updates changing the last box on the "updates" tab to "for any new version" Then reboot and run update again > and the "upgrade" option. Still no luck?
then try
menu > administration > software & updates click the updates tab and press alt + f2 and type in the top box "update-manager -d" (without the quote marks) It should then offer the upgrade option.
Thank you to all contributors to this problem.
I have decided to wait for for 22.04LTS for the next upgrade as I have already installed the new Mate desktop 1.26.
The issue of upgrading without losing the current setup has plagued me since Hoary. Sometimes it works - other times it does not.
After a lifetime in [corporate] Windoze this is still the OS of my choice and this is a small price to pay.