I'd argue that, if you are able to overcome gravity via buoyancy and/or aerodynamic lift, you are not yet in space. If you need to use orbital velocity to stay up, then you're in space. That probably still leaves some room for argument, but it would be a pretty narrow range of altitudes in which to argue.
Vorticity t1_j8y4s2f wrote
Reply to Where does space really begin? Chinese spy balloon highlights legal fuzziness of ‘near space’ by HarpuasGhost
I'd argue that, if you are able to overcome gravity via buoyancy and/or aerodynamic lift, you are not yet in space. If you need to use orbital velocity to stay up, then you're in space. That probably still leaves some room for argument, but it would be a pretty narrow range of altitudes in which to argue.