This is an amazing semi-automatic A.C.A.A.N. effect (the acronym stands for: Any Random Card At Any Numbers' Sum), requiring no stooges or any sophisticated technique.
A case containing a deck of cards is placed by the magician in full view on the table, even before the effect begins. Spectators are asked to point to a card, starting with the suit and then deciding its value through two absolutely free choices of their own. Just to further demonstrate total arbitrariness, they are asked to point to some other value from 1 to 13 and the whole thing, including the previous choices, is noted down on a notepad sheet (or on a blackboard, in case the effect is performed on a stage).
At this point, the spectators are told that they can keep their initial choice of card or change its value to any one of those indicated. Having finally established the card, its position will be determined randomly by the sum of all other values indicated by the audience.
Having taken note of the chosen card and number, the magician draws, without the slightest suspicious movement, the cards from the case (which has been in their sight from the beginning) and points out that it is now perfectly empty (and there are no cards left inside). He begins to count them one by one, showing them to the audience: having arrived at the indicated number, he can only reap well-deserved applause by revealing at that very spot in the deck their chosen card!
1st edition 2023, PDF 13 pages.