If you’re developing an iOS app on Windows or Linux using a cross-platform framework, you would still need a Mac machine to build an archive of your iOS app. There are a couple of options for how to build an .ipa archive if you don’t own a Mac yourself. For example, you could rent a Mac in the cloud.
Another option is to set up a build pipeline on a CI/CD service that offers macOS machines and allows you to connect to the machine running the build. For example, Codemagic enables its users to access the build machine via a graphical user interface using VNC. Start the build, log in to the remote build machine and access Xcode on the machine to configure your code signing settings. You can then push the changes to your repository. From there on, you can set up code signing to receive signed iOS builds. Codemagic offers individuals 500 build minutes free every month, see the pricing information here.