A freely chosen card levitates on top of the deck. Then another card is passed under the levitating card to prove that there is no connection at all, you can look through and see that it is in the air.
Please note that the explanation video has no verbal explanation. It includes a couple of inserted lines of text, and the rest is purely a visual explanation. Building the gimmick will require some time and effort, and you will most likely have to buy some supplies, but it is not particularly difficult to make.
1st edition 2019, length 18 minutes.