Ok, so I just turned on my Pi4 and did my usual apt update, but I got a strange output:
$ sudo apt update
[etc, no errors above this...]
Err:9 http://deb.debian.org/debian bullseye-security Release
404 Not Found [IP: 151.101.62.132 80]
Hit:10 https://ppa.launchpadcontent.net/theofficialgman/flatpak-no-bwrap/ubuntu focal InRelease
Hit:4 https://box64.debian.ryanfortner.dev/debian ./ InRelease
Hit:7 https://box86.debian.ryanfortner.dev/debian ./ InRelease
Reading package lists... Done
E: The repository 'http://deb.debian.org/debian bullseye-security Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
I am a bit confused by this. I am a noob, but I know a bit about bash/apt. I have come across this error before, but only when I tried to add a custom repository, not with an official one. Last time, I fixed this error by deleting that source from sources.list.d but I don's know whether I should because it looks like a vital source. It used to work fine until this morning.
Just in case it matters, here are my system specs:
Board: Raspberry Pi 4 Model B 8GB RAM OS: Debian 11 Bullseye (if you need any more say in the comments)
Any help appreciated!
cd /etc/apt/source.list.d
sudo rm filename.list