ATMs very rarely inform users before they put their card in the slot whether it’s the kind of machine that uses a motor to suck your card into the machine. If yes, then avoiding the machine is a good idea.
The question is, how do you find out in advance whether the machine has a motor? Obviously if you test it on your actual valid bank card that you intend to use for the transaction, you may not get it back.
So my first thought was carry expired old bank cards which can be sacrificed. Stick the card in and if a motor pulls it in, hit the cancel button and try it on the next ATM until you find an ATM that does not suck the card in. This still has issues. The machine can vary well confiscate the card merely on the basis of being expired (thus invalid). Sure, it’s a sacrificial card but I don’t have 100+ such cards to spare. And also those dead cards will have my name on them and the ATM network could blackball my name.
So my next thought is to cut a rectangle from a plastic food container to use as a dummy card. It’s still dicey because criminals are deliberately sticking thin plastic sheets into card slots to cause the next real inserted card to get jammed (this is in fact one of many reasons why legit users should avoid the motorised card slots in the first place). But if you cause things to jam up, you could get treated like a criminal (camera → facial recognition.. etc).
Maybe loyalty cards.. grab a stack of loyalty cards from a grocery store and use those as dummy cards. Better ideas?
I would definitely go with a loyalty card. In case you get hassled about it, you have a plausible excuse: you grabbed the wrong card.