Ion wind

The common reasoning that's given for this is that they looked at his experiments and they said there is a more mundane explanation.

Ionic wind.

Basically, ionic wind is like a high voltage within a system.

It will ionize nearby air molecules.

These ionized air molecules will be pulled towards an oppositely charged electrode.

And on the way, they bump into other air molecules, pushing the surrounding air around, generating thrust.

It's called the ionic wind effect, and you see it in Dyson air purifiers these days.

So they said that's all this is.