I tried to find the binary blobs in Signal for android but it looks like a Kotlin app to me. Maybe these were there at one point but were removed later, who knows.
Come to think of it I’m surprised that we can say “no Google play services” but in the same breath support MicroG as if the client apps have anything to do with which version of Play Services they support.
Sorry but F-Droid allows many apps that use “undesirable” networks and services but for no reason that I can see snuffs out the one wholly supported notification system on literally all android devices. Its plug and play. Its got no place in the “Free” part of FOSS but it’s still intentionally more challenging to get around.
Apparently the packaging requirements for F-Droid are more challenging than just “must be open source” and aren’t for everybody.
https://f-droid.org/en/docs/Inclusion_Policy/
The “no Google Play services” alone are a non starter for many apps. My preferred messenger, Signal, is plenty open source and runs its own notification daemon, but cannot be found on F-Droid. I have to get it via Obtainium instead.
You could also just use a USB drive or even a CDRW drive 🤓 Imagine a CD with dotfiles sharpied onto it like its 2001