OK so let's concentrate the idea here:
You have 57 temperature sensors and 38 solar inverters, producing statistics all the time. They are connected to a network, private or Internet, doesn't matter.
You want a user interface where you can look at all the values. Or you want to look at just the temperature in Bob's room. Or you want to look at solar production at the Fucking (the place name) branch office, there are 13 inverters there.
So what do you do? You give some labels to all those data sources, and tell them: send the data to server at 12.34.56.78.
Then you connect with your mobile app or whatever to the same server, to read out the data.
Completely trivial. Except that you need to come up and implement a protocol to do that. And write the server software which collects the data, and sends it forward to the subscribers. You know, make a list of connections that are subscribers, remember what each of them requested, and every time you get Bob's room temperature, send it to client #123. And send all the Fucking results to that another client. And to make the Fucking use case easier, accept a wildcard so that you can ask for Fucking/* inverters in one go, instead of listing all 13 separately.
You can do all of this yourself, or you can use MQTT. If it's the right tool, use it. Else, don't use.
If you have no idea why in the world would you like to have a server, it sounds like you don't need MQTT.