You're right it has been discussed before
But to summarise; anything that is construed as training will require TSA approval and an appropriate visa if you don't have US citizenship or a green card.
But, there's nothing to stop you from having a passenger flight with an instructor, where you may occupy the LH seat and possibly be invited to take the controls for a while.
A trial flight would normally be considered to fit within these criteria.
Training organisations are obliged to check the eligibility status of all candidates.