Based on the changelogs and available refs, I would say the tech preview was done during 5.10 and first release 5.11.

You can still try to build it with 5.7 however, that version is more than outdated and you should consider updating Qt to more recent version.

I've searched the qtmqtt repository for any commits, tags, or references that indicate compatibility with Qt 5.7 but found none explicitly linked to that version. The earliest commits in the repository date back to early 2017, post-dating the release of Qt 5.7.

I used commands to look through commit messages for mentions of "Qt 5," as well as checking the repository history from its inception to see if there might be any underlying support for earlier Qt versions.

How can I identify a compatible version of qtmqtt that works with Qt 5.7, given that there are no explicit references to Qt 5.7 in the repository tags, branches, or commit messages?

Are there specific methods or tools I could use to trace back the compatibility of this library with older versions of Qt, such as Qt 5.7?

Or, should I be using something else like Mosquitto or something since searching has lead to nothing that provides a solution so far.

Thank you for any help you can provide.