I've been trying to create thin playing cards with my printer. The best result came from 3 layers of 0.1mm thickness. That results in a 0.4mm thick card, which is close to the 0.3mm thickness of standard play cards. And feels nice and bendy in your hand. The biggest drawback is just how much time you must spend on the print, it quickly adds up - I would not use this method for games with more than 20 cards.

0.1mm height.
Do NOT use brim.
Put a pause/color change at layer 1.
The first layer has to be black or very dark, otherwise the card will become transparent.

Because the model is very thin, you might have to adjust the height scale to make sure you get 3 layers.

I have included a waste block that you can place close to the zero-zero corner on the bed.

I would love to hear if you do something with this!

Creality

Ender 3

No

No

200

38