What is not having a dominant foot called?

Solution 1:

'Ambidextrous' is the word.

'ambi-' = both, '-dextrous' = right, so together it is as though both are equally dominant. Usually, your feet (and eyes) follow the same dominance as your hands. So if your hands are both dominant, your feet will both be dominant, too.

But if for some reason your feet have different dominance pattern than your hands, maybe you're left handed but right-footed, then you'd say well right-footed. And if both feet are dominant, then the way to say it is

your feet are ambidextrous.

Solution 2:

Two-footed is used in sports, especially in soccer/football.

Of a footballer: able to kick equally well with either foot. [OED]

Ambipedal is a synonym but it is not a common word like ambidextrous.