An information that I read at some point on the internet, I don’t remember where (not on the Apple website): if you rest your hand on the trackpad while typing, macOS is smart and ignores their movement.
In fact, typing does not matter. Try to do a gesture, any gesture, using the palm. It does not react. A palm and a finger produces the regular mouse moving, like the palm is not there. The same for gestures involving more fingers.
Since your fingers are on the keyboard and you touch the trackpad only with your palms, their movement does not produce clicks or moves of the mouse cursor.
Apple has solved the problem some time ago (maybe this is the reason why they removed the “Ignore accidental clicks while typing” setting), they just forgot to make the information public somehow.