I added a new “Gauges” style for QGIS to my GitLab repository that contains some of my use cases of Geometry Generators.
All info on this new QGIS style, including example files, can be found on https://gitlab.com/GIS-projects/qgis-geometry-generator-examples/tree/master/QML-files/gauges
You can download the entire repository with all my Geometry Generator examples at once: https://gitlab.com/GIS-projects/qgis-geometry-generator-examples/-/archive/master/qgis-geometry-generator-examples-master.zip