Ubuntu20.04换源报错E: Failed to fetch https://mirrors.ustc.edu.cn/ubuntu-ports/....

Reading package lists... Done
E: Failed to fetch https://mirrors.ustc.edu.cn/ubuntu-ports/dists/focal/main/binary-amd64/Packages  404  Not Found [IP: 2001:da8:d800:95::110 443]
E: Failed to fetch https://mirrors.ustc.edu.cn/ubuntu-ports/dists/focal-updates/main/binary-amd64/Packages  404  Not Found [IP: 2001:da8:d800:95::110 443]
E: Failed to fetch https://mirrors.ustc.edu.cn/ubuntu-ports/dists/focal-backports/main/binary-amd64/Packages  404  Not Found [IP: 2001:da8:d800:95::110 443]
E: Failed to fetch https://mirrors.ustc.edu.cn/ubuntu-ports/dists/focal-security/main/binary-amd64/Packages  404  Not Found [IP: 2001:da8:d800:95::110 443]
E: Some index files failed to download. They have been ignored,or old ones used instead.

RK3588开发板，arm64架构，Ubuntu20.04.06 LTS进行 sudo apt-get update 一直报上面错误，源使用的是20.04对应版本focal，且使用arm64架构的ubuntu-ports，换了很多源一直报同样的错，不知为什么。
但点进去该报错链接页面确实不存在，404…

后来多方查找终于解决了！！！
运行：

dpkg --print-architecture

输出：

arm64

运行：

dpkg --print-foreign-architecture

输出：

amd64

貌似是多了amd64这个外部架构，需删除掉它。
解决：

sudo dpkg --remove-archecture amd64

这之后 sudo apt-get install 成功。