XMPP lacks good clients and suffers from fragmentation of protocol standards implementation

• For Android: Conversations is excellent, also on F-Droid if you don't want to use the Google store.
• For iOS/MacOS: Siskin or iOS/MacOS: Monal.
• For Linux/Windows: Gajim or Linux: Dino.

"Protocol fragmentation" is not a valid complaint about XMPP -- it's like complaining that ActivityPub is fragmented; but that's not a problem: you use the services (Mastodon, Lemmy, Kbin, etc) built with it which suit your needs, mostly interacting with that sector of the federation (eg, Lemmy+Kbin), but get a little interoperability with other sectors as a bonus (eg, Lemmy+Mastodon).