MQTT is just a messaging protocol, it’s mostly used for iot purposes like you mention, but can in theory be used for any kind of project.
Never used ejabberd, but one of their selling points are multiprotocol support, so it’s not so weird to support a multipurpose standardized messaging protocol.
Literally how SnowPiercer started, and I am all for it, train based survival here we go!
Currently Endeavour OS, but I mainly daily drive Fedora, because its the right mix between bleeding edge and stable (stableedge?) for me.
I use a mix of Fedora and endeavour, love fedora to bits, but I had some issues that were solved by using endeavour
On my OpenSuse server I had to add :Z after /data in the bind, dont know if it applies to your setup, but it is easy to test and see if it works