cat /etc/apt/sources.list
deb http://deb.debian.org/debian bullseye main
deb http://security.debian.org/debian-security bullseye-security main
deb http://deb.debian.org/debian bullseye-updates main
#deb http://security.debian.org/debian-security bullseye-security main contrib non-free
#deb http://deb.debian.org/debian bullseye-proposed-updates main contrib non-free
# Uncomment deb-src lines below then 'apt-get update' to enable 'apt-get source'
#deb-src http://deb.debian.org/debian bullseye main contrib non-free
#deb-src http://security.debian.org/debian-security bullseye-security main contrib non-free
#deb-src http://deb.debian.org/debian bullseye-updates main contrib non-free

pi@raspi4:~ $ cd /etc/apt
pi@raspi4:/etc/apt $ cd sources.list.d/
pi@raspi4:/etc/apt/sources.list.d $ ls
docker.list  mono-official-stable.list  raspi.list  rpimonitor.list
pi@raspi4:/etc/apt/sources.list.d $