Meson is currently not directly supported by Qt Creator. There is an error message in the report: https://bugreports.qt.io/browse/QTCREATORBUG-18117 , and I am considering the possibility of its implementation.
I am currently using the meson through the "Common Project". Go to "New file or project", "Import project" and there, "Import an existing project." This gives you a dialog in which you can select the files that make up your project.
After that, you will need to edit "projectname.includes" and add include files (one per line). Then you need to edit "projectname.config" and add define (one per line) there.
Finally, you will need to edit the assembly configuration and call the ninja, and not do there.
.