Spiritually, Blender is to FreeCAD what Gimp is to Inkscape or what BMP is to SVG. With Blender you're massaging piles of anonymous polygons so they look right aestheticallY, while with CAD you're composing geometric primitives to make a precise blueprint for a 3D object that just happens to be rendered with polygons. The former is better for art while the latter is better for manufacturing.
Parent's comparison is pretty great, but it shouldn't be "overdone". It's not really the format that's different/a problem (it's not hard to make a blender object from a CAD design - the same way an SVG can be rendered to PNG, and similarly irreversible in both cases), it's the whole design flow.
CAD uses geometry primitives with parameters and exact sizing (e.g. you draw a rectangle of this size, and cut a whole into it this and this offset from one of the corners, and you expand this shape to 3D). As mentioned this can be approximated via geometry nodes, but they are very different in "ideology".
A .step or .stp file encodes the model as mathematical shapes, rather than approximating it with polygons, but it doesn't save the entire parametric workflow or history, only the final result. As far as I know, there is no widely adopted file format that also saves this information.
For architecture, there is Industry Foundation Classes (IFC). IFC is a standard for describing building. FreeCAD supports this natively. There's a tutorial here: https://yorik.uncreated.net/?blog%2F2025%2F002-nativeifc-tut...
Blender has and extension for IFC called Bonsai. https://extensions.blender.org/add-ons/bonsai/
Any there any open CAD file formats that lay a foundation for describing this kind of 3D data without classic triangles?