If you have a Mac and xcode on it you build the IPA and deploy it to your iphone thru xcode. A developer needs to be able to test their own application this xcode just uses your regular devices and let’s you deploy onto them.
The beauty of open-source is that you can build an APK/IPA yourself and be sure that your app - your version is truly not spying on you.
I think most people just take Signal’s devs words for it that it’s the same.
I tried Crossover multiple timea over the last 10 years and I always ended up uninstalling it. It never worked for anything. Not wvwn simple games.