Can't install Syncthing b/c of "release file"

[tag]

• FreedomBox plugged into router.
• Recently bought new kit.
• Running Debian GNU/Linux 10 (buster) and FreedomBox version 21.4.

I’m trying to install Syncthing. I get the following error: “E: The repository ‘Index of /debian-security stable/updates Release’ no longer has a Release file.”

I tried SSH into FreedomBox then running: sudo apt-update
Still no luck.

So, how do I install Syncthing?

[njoseph]

Duplicate of Error installing apps after fresh install of FreedomBox

You can either modify your /etc/apt/sources.list as stated in this answer -

Error installing apps after fresh install of FreedomBox

All the newly built stable images (announcement pending) seem to have bullseye-security listed in the sources.list. So, there is no problem there. It is also best if users use bullseye everywhere in the sources.list instead of stable to allow FreedomBox to automatically upgrade to next stable release bookworm in 2 years in controlled manner. A typical sources.list file should look like: deb http://deb.debian.org/debian bullseye main deb-src http://deb.debian.org/debian bullseye main deb http:…

Or install the latest Pioneer image built for Debian 11 (Bullseye) from here:
https://ftp.freedombox.org/pub/freedombox/pioneer/weekly/

[tag]

When I opened FreedomBox later, it had updated to Debian 11 (Bullseye) on its own (probably through an auto-update). I was able to install Syncthing after that.