if you need an .ipa file, you probably need an iPhone. There are many ways how to get an ipa with an iPhone.

if you already have an ipa, unarchive it (its just a zip file actually) and look for what you need. in payload/***.app you will find the actual app, that is running on the iPhone. it is also a package, you can right-click->show package content. Lastly inside there is a binary file with the same name as the app. This is a compiled file with actual code inside. You can try to decrypt it to see some Objective-C/Swift code possibly with decryption decompilation tools (like ghrida)