@Moem @pparent thanks for the answers, on linux Gajim, Dino are the popular ones, Dino support audio call too. On Android converstion is the best app.
xmpp is the protocol and it is pretty much same popular as matrix. There are pros and cons, both are great however currently the Ubuntu Touch 24.04 does not have any working client. I tested ConverseJS but it does not connect, looks like not using the usual way other clients. No other option available in the UBport app store.
This would be super important to have xmpp support because many people switch to custom roms due to privacy and they use either xmpp or matrix for communication.
Also wireguard VPN client would be great, because many people use opensource firewalls like OPNsense and this one is already phasing out the old openvpn and use wireguard from now on.