Individually, yes, each app cannot obtain much data. But all the apps sell their bit of data to a third party, and buy the resulting profile about you, because they can identify you.
So no, the McDonalds app doesn't know when you got paid directly. But it does know that you bought a cheeseburger in the last two weeks of every month, and it knows that your grocery expenses are higher in the first two weeks of every month, and you tend to eat at a restaurant in the first week of every month, and you take less ubers in the last week of every month; it's not hard to conclude that you get paid at the start of the month.
And that's without your banking app selling your info, which it might do. In which case it knows exactly when you get paid, and your probable current bank balance right now when you place your cheeseburger order.
So no, the McDonalds app doesn't know when you got paid directly. But it does know that you bought a cheeseburger in the last two weeks of every month, and it knows that your grocery expenses are higher in the first two weeks of every month, and you tend to eat at a restaurant in the first week of every month, and you take less ubers in the last week of every month; it's not hard to conclude that you get paid at the start of the month.
And that's without your banking app selling your info, which it might do. In which case it knows exactly when you get paid, and your probable current bank balance right now when you place your cheeseburger order.