"Your Apple Account could not be used to sign in to Apple Account (34608)"

My iPhone 14 plus iOS 18.7.1 won't let me sign in to my Apple Account or iCloud

I tried iCloud for Windows, but it says I have to setup iCloud on a Mac or iOS.

I can sign into Apple.com and iCloud.com with the same email and password. My account settings show the correct email address and phone number. My iPhone shows up in Devices. There is an image on the account that says, "iCloud web-only access", which might be the problem.

How do I allow my iPhone to sign into my iCloud account?