修改 /etc/apt/sources.list.d/ubuntu-esm-apps.list
deb https://esm.ubuntu.com/apps/ubuntu focal-apps-security main
deb https://esm.ubuntu.com/apps/ubuntu focal-apps-updates main
将 focal 改为 bionic 解决了
deb-src https://esm.ubuntu.com/apps/ubuntu bionic-apps-security main
deb-src https://esm.ubuntu.com/apps/ubuntu bionic-apps-updates main