Can't upgrade Pi 3 LTS

ruscorp

Can anyone help me figure out why I can't update my orange pi 3 LTS?

orangepi@orangepi:~$ sudo apt update && sudo apt full-upgrade

Hit:1 http://archive.debian.org/debian-security stretch/updates InRelease

Hit:2 https://download.docker.com/linux/debian buster InRelease

Hit:3 http://mirrors.tuna.tsinghua.edu.cn/debian buster InRelease

Hit:4 http://mirrors.tuna.tsinghua.edu.cn/debian buster-updates InRelease

Ign:5 http://mirrors.tuna.tsinghua.edu.cn/debian buster-backports InRelease

Hit:6 http://mirrors.tuna.tsinghua.edu.cn/debian-security buster/updates InRelease

Err:7 http://mirrors.tuna.tsinghua.edu.cn/debian buster-backports Release

404 Not Found [IP: 101.6.15.130 80]

Reading package lists... Done

E: The repository 'http://mirrors.tuna.tsinghua.edu.cn/debian buster-backports Release' no longer has 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.