Today I tried to install Samba on Charlene and received an endless supply of repository errors. This is because the Buster repository has been archived.
It turns out that you have to update /etc/apt/sources.list and comment out everything in /etc/apt/sources.list.d/raspi.list
Remove (or comment out)
deb http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi
deb http://www.linux-projects.org/listing/uv4l_repo/raspbian/stretch stretch main
Add
deb https://legacy.raspbian.org/raspbian/ buster main contrib non-free rpi
deb http://archive.raspberrypi.org/debian buster main
In /etc/apt/sources.list.d comment out everything in raspi.list
. . . and run sudo apt update.
Some repositories will still fail.