refer to:
https://mirrors.tuna.tsinghua.edu.cn/help/debian/
bullseye 的mirror:
# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释 deb https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye main contrib non-free # deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye main contrib non-free deb https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-updates main contrib non-free # deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-updates main contrib non-free deb https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-backports main contrib non-free # deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ bullseye-backports main contrib non-free deb https://mirrors.tuna.tsinghua.edu.cn/debian-security bullseye-security main contrib non-free # deb-src https://mirrors.tuna.tsinghua.edu.cn/debian-security bullseye-security main contrib non-free
具体用法一目了然：
