tl;dr
You can use this command to get Signal installed in an Ubuntu distrobox with the required packages—and a systemd service that automates updates for all distroboxes.
curl -sL -o /tmp/signal-install.sh https://codeberg.org/shampan/signal-distrobox/raw/branch/main/signal-install.sh && bash /tmp/signal-install.sh && rm /tmp/signal-install.sh
Background
So as someone who moved from a system that had native support for .deb packages, one of first things I missed was a native Signal installation.
Why not the Flatpak?
The flatpak is not officially supported and has had multiple database corruption and stability issues in the past. Its current approach stores encryption keys in plaintext by default, while support for secure, encrypted key backends remains experimental.
Distrobox
You can of course install it in a Ubuntu distrobox, but the default installation is missing a few packages for it to launch or screenshare.
Automated installer
I’ve made and automated installer that installs signal into an Ubuntu distrobox with additional packages required for stability, and screensharing. I’ve also had the script include the systemd service to automate updates for all distroboxes.
If you already have distrobox updating automated or would not like automatic updates you can just create the signal container by itself:
distrobox assemble create --file “https://codeberg.org/shampan/signal-distrobox/raw/branch/main/signal.ini”
Hope this helps.