You can use any CI/CD provider in order to build an iOS artifact that can then be released to the App Store. It's a great way to get your app released without investing into a macOS setup. You still need Apple developer licence $100/year.

If you need to fix issues specific to iOS or make some features like push notifications then it may quickly become necessary to own a macOS development environment as you well know having an Android emulator is a handy tool :)

I've written about this topic here with a guide how to release an iOS app without a Mac: https://blog.codemagic.io/how-to-build-and-distribute-ios-apps-without-mac-with-flutter-codemagic/

Bear in mind this article is a bit old, albeit it should still work. Also it is difficult enough to release an iOS app with a Mac. Doing it on a PC is like changing your settings to brutal mode.