编辑 /etc/apt/sources.list 文件
参考 debian | 镜像站使用帮助 | 北京外国语大学开源软件镜像站 | BFSU Open Source Mirror
记得备份原文件，然后把内容清空改成以下内容：
# 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.bfsu.edu.cn/debian/ bookworm main contrib non-free non-free-firmware
# deb-src https://mirrors.bfsu.edu.cn/debian/ bookworm main contrib non-free non-free-firmware
deb https://mirrors.bfsu.edu.cn/debian/ bookworm-updates main contrib non-free non-free-firmware
# deb-src https://mirrors.bfsu.edu.cn/debian/ bookworm-updates main contrib non-free non-free-firmware
deb https://mirrors.bfsu.edu.cn/debian/ bookworm-backports main contrib non-free non-free-firmware
# deb-src https://mirrors.bfsu.edu.cn/debian/ bookworm-backports main contrib non-free non-free-firmware
deb https://mirrors.bfsu.edu.cn/debian-security bookworm-security main contrib non-free non-free-firmware
# deb-src https://mirrors.bfsu.edu.cn/debian-security bookworm-security main contrib non-free non-free-firmware
# deb https://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
# # deb-src https://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
另外不是很推荐使用 apt 安装 steam，建议使用 flatpak。不过这两种做法各有优缺点，后者的优点是和系统隔离，不用担心依赖库版本问题。