A mahjurah literal sense is physically or logically possible, but ordinary speech no longer employs the expression in that narrow sense in the relevant context. Established convention identifies what the speaker would normally mean.
Thus, “setting foot in a house” refers to entering it. A person cannot avoid that interpretation simply because shoes, a vehicle, or another means of entry prevented bare-foot contact with the floor.
This differs from an impossible literal meaning. In an abandoned usage, the literal action may be possible but is not the normally intended meaning. That distinction will matter when literal and figurative senses compete.