If you're asking "Can I use the same Dart code I wrote on Windows when I develop on macOS?" the answer is yes: Flutter and Dart run on both, and consume the same source code regardless of platform.
If you're asking "Can I develop for both iOS and Android using only Windows or Linux?" then the answer is no: Flutter relies on Apple's developer tools under the hood to build, archive, and upload apps to the App Store. Apple only makes Xcode available for macOS, so a Mac is a requirement for iOS development with Flutter. Android development works on all three platforms.
You can develop for both Android and iOS on a macOS development machine, since both build environments run on macOS. I believe there are several online macOS virtual machine providers that specifically target developers, but I haven't got any experience using them myself. It's possible someone else on the list has though!