我的 Ubuntu Server 20.04 在 Raspberry Pi 4 上运行。现在由于某种原因我收到错误消息：无法获取 <sources.list links> 404 Not Found [IP: <some_ip>]。我尝试了一些解决方案但无法修复它。
错误终端输出（apt更新）：
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/focal/main/binary-arm64/Packages 404 Not Found [IP: 91.189.91.38 80]
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/focal-security/main/binary-arm64/Packages 404 Not Found [IP: 91.189.91.38 80]
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/focal-updates/main/binary-arm64/Packages 404 Not Found [IP: 91.189.91.38 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.
我的sources.list文件：（我已经从这个平台的解决方案更新了这个列表）
###### Ubuntu Main Repos
deb http://us.archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ …