You're right. It seems I am eating my words on that item, the `--no-sandbox` flag does seem to be on in most Linux installs. From context and search, it looks necessary for it to work on Debian.

Can confirm with `cat /usr/share/applications/signal-desktop.desktop`.

This still would require a pretty sophisticated attack to take advantage of, but I wouldn't rule it out as an attack surface. (We regularly see iPhone exploits that attack font and image rendering, after all.)

I'll amend my post given this.