It looks like the mirror of the Ubuntu archive you are using is not mirroring the release which you are trying to upgrade to. Please switch to an official mirror of the Ubuntu archive and then try the upgrade again.
>From VarLogDistupgradeMainLog.txt: 2021-03-29 15:10:51,087 DEBUG url_downloadable: http://ubuntu.mirror.datamossa.io/ubuntu//dists/focal/Release 2021-03-29 15:10:51,087 DEBUG s='http' n='ubuntu.mirror.datamossa.io' p='/ubuntu//dists/focal/Release' q='' f='' 2021-03-29 15:10:51,125 DEBUG error from httplib: 'HTTP Error 404: Not Found' ** Changed in: ubuntu-release-upgrader (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1921673 Title: An unresolvable problem occurred while calculating the upgrade. This was likely caused by: * Unofficial software packages not provided by Ubuntu Please use the tool 'ppa-purge' from the ppa-purge package to remove software from a Launchpad PPA and try the upgrade again. If none of this applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. If you want to investigate this yourself the log files in '/var/log/dist-upgrade' will contain details about the upgrade. Specifically, look at 'main.log' and 'apt.log'. Comment: I don't know what this means. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1921673/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
