sudo apt-get update failed.

when i “sudo apt-get update failed”,it show me(E:Failed to fetch http://ppa.launchpad.net/wengxt/fcitx-nightly/ubuntu/dists/xenial/main/binary-arm64/Packages 404 Not Found. E:Failed to fetch http://ppa.launchpad.net/chromium-daily/stable/ubuntu/dists/xenial/main/binary-arm64/Packages 404 Not Found. E:Some index files failed to download. They have been ignored ,or old ones used instead.)

i had change the URL ,but it didn’t work,also have some Err like these.
How can i fix it?thanks.

I wonder if basic networking is failing (specifically DNS). One of the nvidia.com IP addresses is “216.228.121.209”. Which of these work, which fail?

ping 216.228.121.209
host nvidia.com

If “ping” works, but “host” fails, you simply need to configure DNS in order to get names converted to dotted-decimal format IP addresses. If ping fails, then the router is not forwarding.

Looks like these xenial repositories are no longer available:https://launchpad.net/~wengxt/+ppa-packages, nor http://ppa.launchpad.net/chromium-daily/stable/ubuntu/dists/.

You may just disable these repositories, or find the new repositories path if any.

“ping” and “host” can work well
what should i do …

Sounds like @Honey_Patouceul has the correct answer. You might comment them out in “/etc/apt/sources.list” or use regular apt commands to disable those. After that and “apt update” to make the changes effective, you might post what packages you need which are no longer available.