For the z88 export the FemMesh must be passed to its Python wrapper which will increase the counter upon construction and decrease it upon destruction. If the counter becomes 0 the FemMesh will be destroyed too which causes a crash.
To fix the crash the counter must be increased and safely decreased after the lifetime of the Python wrapper.
This fixes https://github.com/FreeCAD/FreeCAD/issues/23380
8944fd7d5e