$ sudo do-release-upgrade
Checking for a new Ubuntu release
There is no development version of an LTS available.
To upgrade to the latest non-LTS development release
set Prompt=normal in /etc/update-manager/release-upgrades.
I changed to normal and did release-upgrade:
Updating repository information
No valid sources.list entry found
While scanning your repository information no entry about focal could
An upgrade might not succeed.