Do not trust the FUD.
I've been using XMPP since I had a smartphone (I was late to the party, around 2015) and never needed a persistent connection or had issues with multi-device use. https://xmpp.org/extensions/xep-0313.html solves both and the first version is from 2012.
E2EE via opengpg has been there since the beginning of XMPP, and via OMEMO (signal-like) for 7 years now, just like HTTP file upload.