According to the site, the latest versions of Qt for Windows are still being built with libpq version 9.1.9, which is no longer supported.
Please update the PostgreSQL library used to build new Qt releases.
The upgrade is also necessary so that you can use forward-only mode in SQL queries.
See commit: 210952 f99d2b21b8fc867f0ed21dcbfa47865ad013db97
Currently, to use the forward-only mode, you need to recompile the QPSQL plugin with libpq library version at least 9.2.