[Bug 1897943] Re: Initally upgrade stopped for extra PPAs which I removed and tried upgrade again without rebooting. It generated this error as unresolvable error.

[Expired for ubuntu-release-upgrader (Ubuntu) because there has been no activity for 60 days.] ** Changed in: ubuntu-release-upgrader (Ubuntu) Status: Incomplete => Expired -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu.

[Bug 1897943] Re: Initally upgrade stopped for extra PPAs which I removed and tried upgrade again without rebooting. It generated this error as unresolvable error.

Removing from software manager is not the same things as removing the packages from the PPA. You still have packages installed from the oibaf- ubuntu-graphics-drivers-bionic PPA. Those packages are preventing the upgrade from being calculated. You need to reenable the PPAs and then use the tool