Sudo apt-get update doesn't work

too many errors to list here, but here are a few of them, everything is "error" or "not found" when i try to update

Err:52 Index of /ubuntu-ports impish-updates/universe arm64 liblightdm-gobject-1-0 arm64 1.30.0-0ubuntu4.21.10.1

N: Updating from such a repository can't be done securely, and is therefore disabled by default.

Anyone have any ideas what i can do? Thank you (Ubuntu mate on Raspberri Pi 400)

Ubuntu 21.10 (impish indri) is end of life which is why it isn't there. This applies to all flavors of Ubuntu too, such as Ubuntu-MATE.

After reaching EOL, mirrors are free to drop support for the release, and the main archive is moved, other archives are just dropped.

This maybe helpful - EOLUpgrades - Community Help Wiki but you appear to be using a port thus it can be more complex. Perform your release-upgrade before EOL for best results.