Question: Is there a free to use chat/instant messaging server that supports #XMPP ? Alternately, Is there any kind of chat/IM softeate that runs on both the #Windows and #MacOS desktop and that DOES NOT require entering a phone number or using a mobile phone for setup (so, no WhatsApp/Telegram/Signal - if it requires a phone or phone number for setup or use then it is off the table).

Additional info: I already know that you can run #prosody on a server you control but the problem is that you then have to know how to secure it, and there is one user in particular that seems to have an ever-changing IP address (he uses T-Mobile's home internet service - if you know about that then you understand the problem). So you can't just set up iptables and allow his address because that address may be different from session to session, and since the start of February it seems it may be different for each application he uses, or each web site he visits (for example he can go to one of those sites that shows the IP address you're coming from and it will show a different address on each such site he visits). It's almost as though #T-Mobile is suddenly forcing all connections to go through something like the #Tor network. Which on the one hand is probably great for #privacy but not great if you are trying to get into a server that is configured to let you in based on your IP address.

We used to use Google Chat/Talk until they started requiring oAuth authentication (which most XMPP Clients don't support) and really would kind of prefer not to use Google for this purpose anyway. So, just wondering what alternatives might exist.

(And before anyone suggests direct messaging in #Mastodon, the issue there is whenever you send a private toot it throws you into the "Direct messages" section and then you lose your place in your home timeline. Mastodon REALLY needs to figure out how to save your current place in the timeline so you can easily get back to it, though that may in part be because the instance I use is running Mastodon v3.2.1 which I guess is rather old).