What prevented Electrum from entering f-droid?
There is an open RFP, but it looks like noone wanted to do the effort of writing a build recipe so far
Are there other cryptocurrency applications that have not yet entered this site for a similar reason?
There are many apps that have complicated recipes where help from people that understand the code is needed. Be it crypto related or others.
No matter the build steps are complicated or not, someone needs to write a build metadata for it. No one rejected the app for a reason.
Some topics about this application are from at least four years ago
Is this (mycelium-com /wallet-android) also open source?