Cannot upgrade to 20.04

[Sonder Peters]

Upgrade cannot be calculated. I've removed all sources besides the top two Canonical ones and it still doesn't work.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.38
ProcVersionSignature: Ubuntu 5.4.0-48.52~18.04.1-generic 5.4.60
Uname: Linux 5.4.0-48-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.17
Architecture: amd64
CrashDB: ubuntu
Date: Wed Sep 30 18:42:23 2020
InstallationDate: Installed on 2019-03-22 (557 days ago)
InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-09-30 (0 days ago)

[Brian Murray (brian-murray)]

This is due in part to the package gcc-10-base which you have installed from a third party repository. Please remove that package and any others from that third party repository using the tool 'ppa-purge' from the package 'ppa-purge' and try the upgrade again.

[Launchpad Janitor (janitor)]

[Expired for ubuntu-release-upgrader (Ubuntu) because there has been no activity for 60 days.]