先上结论

m1芯片的mac应使用以下源（适用20.04版本）：

deb http://mirrors.aliyun.com/ubuntu-ports/ focal main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse

再讲原因

因为架构的原因，在x86和arm下ubuntu所使用的源是不同的，两者无法混用

在Intel或Amd处理器下，通过Docker安装的ubuntu自带的源为

deb http://archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse

而在m1芯片下则为

deb http://ports.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse

区别就在于前面的archive和ports

以阿里云的镜像源为例，在阿里云镜像的官方网站上为ubuntu 20.04提供的源为

deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse

不难看出，只需将域名后的ubuntu改为ubuntu-ports即可。

此外，再提供一个可以直接在命令行中使用的换源命令

cd /etc/apt && mv sources.list sources.list.bk && echo -e " deb http://mirrors.aliyun.com/ubuntu-ports/ focal main restricted universe multiverse\n deb http://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted universe multiverse\n deb http://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted universe multiverse\n deb http://mirrors.aliyun.com/ubuntu-ports/ focal-proposed main restricted universe multiverse\n deb http://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse\n deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal main restricted universe multiverse\n deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted universe multiverse\n deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted universe multiverse\n deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-proposed main restricted universe multiverse\n deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse" > sources.list