FWIW on boats there have been a number of experiments which generally 'prove' that they is more resistance from a freewheeeling prop than from a stopped or locked prop.
For this (and a couple of gearbox related reasons) it is not unusualy for some yachts to have propshaft brakes fitted.
In an aircraft the same theory must hold good but there are differences - obviously density - although as the prop is sized to absorb the engines power this should not have an effect. The other obvious difference3 is the speed at which the prop rotates. In the boat tests the prop was genuinely freewheeling, in an aircraft it is driving the engine and so not rotating anything like as fast. As a starter motor can pretty much do the same then it is drawing a little (one to two horsepower) power from the aircraft's path.
So the boat case is much more like an autogyro in aircraft terms.
So a stopped aircraft prop creates pure drag, a slowly rotating one probably creates slightly more - but the difference is probably too small to really notice unless conducted under very still and carefully controlled conditions.
Which largely means it is probably not worth the trouble!