EDIT: LONG POST, my opinion are backed on years of interest in the topics as well as first hand experience.
I'll go Windows x Android first:
Windows is a privacy nightmare. You can try and fight it but you can and will break things along the way. So I'll basically advise you to use anything else.
Android in the other hand has some options to flash custom ROMs and thus you can change what's running. But you're stuck with /e/ OS if you want real privacy without giving up on almost everything Google, banking apps, etc. There are other Android forks but most of them focus on security, features, gimmicks, etc. So at least there you have a good amount of control. You can use Android with KDE Connect for actually good cross device features in my personal opinion.
macOS iOS:
These are fully controlled by Apple. Sure, Apple goes hard against 3RD PARTY tracking, but does not tell you you need to switch off 1st party tracking within multiple settings pages (own experience). There have been some reports about macOS sending hashes of photos from a local account with no iCloud login, but that was fixed quickly, even though I've been skeptical. But this video by Techlore actually explains things really good.
MY conclusion?
I'd say the most private would be Android x Linux with KDE Connect.
2nd place is iOS with proper settings x Linux with KDE Connect. (For real, this tool gets you cool cross device sync.)
3rd place would be iOS x macOS both on privacy friendly settings if you, like me, rely on proprietary stuff. Xcode and iOS development can only be done on macOS and thus I'll stick to this combo. Fedora will always have a special place in my heart and on my SSD though.
So which level of these you want to pick definitely come down to how much you rely on what software and what you can afford. I hope I could help.