## Where are your apt repository sources configuration stored
## see repositories listed in /etc/apt/sources.list
## and those in *.list in /etc/apt/sources.list.d/
grep -v ^# /etc/apt/sources.list | grep -v ^$
(command output - for my machine)
deb http://sg.archive.ubuntu.com/ubuntu/ focal main restricted
deb http://sg.archive.ubuntu.com/ubuntu/ focal-updates main restricted
deb http://sg.archive.ubuntu.com/ubuntu/ focal universe
deb http://sg.archive.ubuntu.com/ubuntu/ focal-updates universe
deb http://sg.archive.ubuntu.com/ubuntu/ focal multiverse
deb http://sg.archive.ubuntu.com/ubuntu/ focal-updates multiverse
deb http://sg.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu focal-security main restricted
deb http://security.ubuntu.com/ubuntu focal-security universe
deb http://security.ubuntu.com/ubuntu focal-security multiverse
deb https://download.sublimetext.com/ apt/stable/