This may have been answered elsewhere, but coming across it, I've had decent luck using 'Projected' plan profile in 'Wall Selection Settings', using 'Outlines' to control the footing line. If necessary, you can change the Floor Plan Cut Plane Settings to cut through the stem wall (and control the stem wall line weight with the cut line pen).
Using a slab or a separate wall profile for the footing is one good solution, because there are instances where the stem wall needs to break whereas the footing is continuous. If you are trying to shown a key between the stem and the footing in section, you could do a stem wall with a key (complex profile), and if you want to get carried away, 'Subtract' via SEO from the footing.
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macOS Catalina Version 10.15.5
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