Apple Card Customer Agreement Updated for 'Upcoming' Savings Account Feature

Define "high yield" in high yield savings. If it's Marcus' 3%, I must remind you that T-bills offer 4+% and the interest from them is exempt from state income tax.
https://www.bloomberg.com/markets/rates-bonds/government-bonds/us
So most folks looking to invest more than $1K would be better served by opening a brokerage account and buying T-bills. And then maybe getting their credit card from that brokerage instead. Fidelity, e.g., offers a flat 2% on everything cash back card.

Have you actually done this other than through a mutual fund or money market instrument? Have you ever opened a brokerage account for the sole purpose of doing what you are proposing? Most people will not be better served with direct purchases through a brokerage account. You ignore liquidity issues, minimum invest requirements on certain instruments and clearing time and procedures.

You are also ignoring interest rate risk inherent with not holding a bill or bond for full term. If you bought 1 yr bills six months ago you have lost badly. In fact, you have less than when you started. $1 in t-bills bought six months ago is worth 97 cents right now and that does not even consider transaction costs. There is an inverse relationship between interest rates and principal value. One goes up, the other goes down.

It is also unlikely someone dealing in minimum denominations can tie their money up for the periods required. Oops, I need that money next Friday because my water heater failed and it is December and this isn't Florida. What do you mean? Fine, but you are only getting 97 cents back for each dollar you put it.

A simple interest savings account is often the instrument of choice due to convenience, liquidity and zero or close to it transaction costs.

Your statement is so generalized that its value is questionable. Every individual's situation and constraints are different. There is no "one size fits all" with this which is why professional advice is important.

Define "high yield" in high yield savings. If it's Marcus' 3%, I must remind you that T-bills offer 4+% and the interest from them is exempt from state income tax.
https://www.bloomberg.com/markets/rates-bonds/government-bonds/us
So most folks looking to invest more than $1K would be better served by opening a brokerage account and buying T-bills. And then maybe getting their credit card from that brokerage instead. Fidelity, e.g., offers a flat 2% on everything cash back card.

You may be right, but a lot of people have Apple Card because it is easy. This saving account would also be easy. That convenience does have value.

it would be nice if there was an option to add funds from a debit card in the wallet app

You can do this already.

Irrelevant because from my reading everyone on MacRumors are independently wealthy original Apple shareholders who pay their statements in full every month.

You don't have to be independently wealthy to pay off your monthly balance. You just have to have enough discipline not to charge more than you can afford to pay. This is something I've learned the hard way. I used to think a credit card limit was like a bank account balance. It was money that I could spend.

This is what I do. I buy individual t-bills and a few bonds (> 1 year maturity). Min is $1000. It’s easy to do auto-roll for those who want it. And if you will need the money sooner than 4 weeks (min T-bill maturity) then it can be left in the money market fund.

You are ignoring principal and rate risk or at least not mentioning it.

I get it and employ similar strategies. Much of that behavior is enabled by my personal finances and what I have managed to accumulate and the fact most of my financial responsibilities to others have been satisfied leaving me with less constraints and a higher level of liquidity. It's just not practical for most people.

Save money by spending money, brilliant!