Everything I've seen says that it's been made as difficult as humanly possible to develop and distribute iOS apps without a Mac. However, it is - in theory - possible, though using Windows is probably going to push the limits or "possible" quite a bit:
How to develop and distribute iOS apps without Mac with Flutter & Codemagic | Codemagic Blog[
^]
It may be simpler is you develop a Xamarin app which works on iOS, Android and Windows - at least you can test the BL / DL sides without any real Apple hardware before you start with the PL.