OpenEMS is FTDT electromagentic solver where simulation is defined in Matlab files, also it's possible run it using Octave.
To simplify geometry, meshing and simulation settings I developed this GUI plugin for FreeCAD.
Project github: https://github.com/LubomirJagos/FreeCAD-OpenEMS-Export
I checked the PySide, it looks to me that I've got only PySide2 (I use mint 20, no support for old qt4 and PySide) so if these are not compatible then this is the issue.