if you need 3 pci-e cables, like for the ftw3 model, then you should be able to daisy chain two of them from one cable.  But I think most people will advise you against doing that, especially with how finicky the ftw3 model is as of late it seems.

You can daisy chain 2 of the 3 PCIe power connectors, but don't do all three on one cable.

Wife's 3090 FTW3 Ultra hybrid ran from 2 cables for over a year on SF750 before I finally tracked down a 3rd dedicated cable. Short answer, 2 cables for a 3 connector card is fine. I would suggest at least 850W for a build with a big pp gpu though. My preference, but yeah the SF750 is also fine for a 3090 + 5900X so just use your best judgment if you plan to overclock at all. Your life is in their hands dude