See https://github.com/procitec/qtcreator-sphinx-plugin/blob/v21.2.2/RELEASENOTES.md for release notes.
To use the plugin you need QtCreator 5.0.3 from https://download.qt.io/official_releases/qtcreator/5.0/5.0.3/installer_source
(builded against Qt 5.15.2)