I get almost 4.6% and am not tied to Apple's ecosystem, so I doubt banks care.

Well it's through Goldman Sachs, so no

Nah it's just a partnership with Goldman.

I like how Goldman directly offers only 3.90%.

https://www.marcus.com/us/en/savings

Seems like they want people to go via Apple.

Or that Apple is trying to grow market share by offering a higher rate.