修改 sources.list文件成以下这样:

deb http://deb.debian.org/debian buster main contrib

deb http://deb.debian.org/debian buster-updates main contrib

# security updates
deb http://security.debian.org buster/updates main contrib

The enterprise repository:

cat /etc/apt/sources.list.d/pve-enterprise.list
deb https://enterprise.proxmox.com/debian/pve buster pve-enterprise

输入以下命令

apt update

如果没有任何错误 就可以开始更新了

apt dist-upgrade

如果上面的方法失败可以将/etc/apt/sources.list文件修改成下面的内容

 deb http://ftp.debian.org/debian buster main contrib
 deb http://ftp.debian.org/debian buster-updates main contrib
 PVE pve-no-subscription repository provided by proxmox.com,
 NOT recommended for production use
 deb http://download.proxmox.com/debian/pve buster pve-no-subscription
 security updates
 deb http://security.debian.org/debian-security buster/updates main contrib

完成后依旧输入

apt update

apt dist-upgrade

开始更新