Good point. I’m not sure if IzzyOnDroid considers the CC license to be “free as in freedom” but even if they do, they allegedly have a 30 MB limit per application, and the most recent SN apk is just under 100 MB.
Signal’s approach is useful if the goal is to avoid being tracked by Google without losing out on the convenience of auto-upgrades, but it’s still bad in that they could theoretically introduce a client-side vulnerability that nobody external would have a chance to audit.
You can also use Standard Notes via the web app, which can be installed as a PWA. And even though it’s not FOSS anymore, the source is at least kept up to date.