That's why ubuntu newest source list should be in pop os source list.
nano /etc/apt/sources.listHere is the source list of ubuntu latest version,and this sources.list
```bash deb http://archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse deb-src http://archive.ubuntu.com/ubuntu/ focal main restricted universe multiversedeb http://archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse deb-src http://archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse deb-src http://archive.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse deb-src http://archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
deb http://archive.canonical.com/ubuntu focal partner deb-src http://archive.canonical.com/ubuntu focal partner
```bash
sudo apt-get update
sudo dpkg -i package_file_name