A special effect, LOL. Right foot on something that can hold all of him, and the left one is barely atop what looks like a platform. Possibly the same thing but without that big show hiding it all. So maybe it's not a special effect where he's levitating. At least he's got the sonic screwdriver and possible constipation-face acting going on. Amazing how the only time we got crappy jokes was in that 1999 CiN special... and the 2023 one, indirectly and based on the budget-stretch situation in 1963 that promoted an iconic decision of brilliance.