Bitcoin is a CBDC in self custody. A fully transparent block chain is very dangerous in times we live now, we see more and more mass survailance, AI is also in play, they want to know everything about your transactions and your finance. Bitcoin is not fungible which is the most important characteristic of good money. We see already tainted coins, they freeze funds when coins have a suspicious history etc. So no Bitcoin is wrong!
SimpleX is not censorship resistant, not sure about Session but they seem to have money issues, PFS was a huge issue etc. Nostr has privacy issues so no, XMPP is still the one I use and will use with tons of others 😀
Matrix uses a way more resources but can be nicer for communities. Signal you can't self host. I don't know Iris. Since I use XMPP for a long time I have all friends on there and also company contacts
If you are looking for a good mobile Monero wallet. Check out Monfluo. Very easy to use, tons of features and the sync process is fantastic. I use it with my https://monero.st node and it works great.
For servers there is Prosody or ejabber. Both are super easy to install and doesn't need lot of ressources. You can run it on a 512MB RAM VPS.
For clients there are also many options. I use Cheogram because I use XMPP for the VOIP service jmo.chat as well. There is also Conversation, Pidgin, Gaijim etc.