iPodDilicious wrote:
The monthly plan is just a way to spread your purchases over a fixed period of time like when you buy an iPhone and paying in 12 installments. There isn’t anything complicated about that. It just happens that they offer a 3% cash back with the monthly plan when paying with an Apple Card.
It is quite complicated. Perhaps Apple's slick marketing has been successful in making you think otherwise. This is money that Apple is paying you, so you can be sure they are going to be tracking it very closely.
After all, you got to this support forum from a link in Products you can buy with Apple Card Monthly Installments. And judging by your earlier quote of "For every purchase you make with Apple Card, you can receive a percentage of your purchase back in Daily Cash: Get 3% back on everything you buy from Apple", you must have gotten to that page via Get unlimited Daily Cash with Apple Card.
That last page seems to be the clearest explanation. It says "3% Daily Cash on all purchases at Apple" and then has a special section dedicated to instalments, listing which products are eligible. Perhaps AirTags will show up on the document eventually. If you want them, buy them and see if you get the 3%. But otherwise, any kind of instalment purchase is special and is going to have special rules. You couldn't ever purchase a gift card with instalments, for example.