Matrix not available on Debian 11?

Problem Description
Matrix Synapse not available on fresh FreedomBox installation.

Steps to Reproduce

  1. Install FreedomBox weekly image.
  2. Setup, but don’t enable “Frequent Feature Updates” (backports).
  3. Go to Matrix Synapse application page.

Expected Results
Allow me to install Matrix Synapse.

Actual results
See the message “This application is currently not available in your distribution.”

Screenshot

Information

  • FreedomBox version: You are running Debian GNU/Linux 11 (bullseye) and FreedomBox version 21.8. FreedomBox is up to date.
  • Hardware: A20 OLinuXino LIME 2 (Pioneer Edition)
  • How did you install FreedomBox?: FreedomBox Pioneer Edition Weekly Image

Matrix Synapse is indeed not available in Debian 11. I believe, this was a conscious decision by the Debian packager due the changes happening in Matrix ecosystem + Debian stable’s nature.

However, matrix-synapse is now present in bullseye-backports, so matrix-synapse should be installable if one is on bullseye and has selected Frequent Feature Updates (i.e., backports) (System/Update page). Presumably Frequent Feature Updates will be needed to install matrix-synapse for the life of bullseye as stable.

/etc/apt/preferences.d/51freedombox-apps.pref still refers to buster-backports. We will need to update it for bullseye-backports.

Issue: matrixsynapse: Install from bullseye-backports (#2122) · Issues · FreedomBox / FreedomBox · GitLab

I forgot about apt preferences and I see matrix-synapse pinned to buster-backports in 51freedombox-apps.pref, but I somehow ended up with v1.42 from bullseye-backports when I went through auto-update from buster to bullseye:
matrix-synapse/bullseye-backports,now 1.42.0-1~bpo11+1 all [installed]