I am translating a 3D visualization lab from ArcMap to QGIS 3.22. The lab is very simple; draping imagery over a DEM and showing 3D points that are earthquake epicenters underneath the terrain.

The problem I am facing: In ArcMap, we were able to vary the symbology of the 3D points based on their magnitude values. The instructions are written up here:

"To do this, right-click on the eq\_3D layer name and choose Properties → Symbology. Next to the symbol, click the Advanced button and from the drop-down menu, choose Size, then choose and click the calculator button to open the Expression Builder. We want to scale the symbols proportionally to magnitude, but the units for magnitude are numerically small compared to the size (in meters) of our desired symbols, so use an expression like [Magnitude] \* 500".

Simple enough!

In QGIS however, it does not seem possible to change the proportions of 3D point symbols based on some value. I have been doing lots of Googling, but haven't seen anyone asking this question. In the 3D Symbol tab in Properties, I attempted to type in expressions into the Radius box, or to do some sort of rule-based 3D symbol but to no avail. To be fair, my expression-writing is not particularly strong, so I could be doing it wrong.

Do you know of any ways to vary the proportions of 3D point symbols in QGIS 3.22 (LTR)?