iMazing is a great app, but there's a lot of misunderstanding on how exactly it works (not just here, but across the web).
iMazing can either:
- Download an app through your purchase history, and then install it.
- Install an app that you've previously downloaded to the computer.
iMazing cannot:
- Extract an app from an iPhone to put on another iPhone, at least not since iOS 8.
- Install an app that you didn't download from your account (cannot use someone else's .ipa file).
Background:
An app can be removed/delisted from the App Store, but still be able to be downloaded through your purchase history (App Store -> Account -> Apps -> Not on this iPhone). Not many people know that; they just search the App Store, see it's not there and think they can't get it anymore. Then they see iMazing can do what they want, but it's really just downloading the app from their purchase history (which they could have just done on their iPhone), or they lucked out and already had the app’s .ipa file on their computer somehow (i.e. from when iTunes used to download them).
In some rare cases, an app can be completely removed from the App Store. When that happens, your purchase history nor iMazing can help (unless you already have the app downloaded/archived on your computer).
For TikTok, the app has been banned from the App Store in the US. It's not possible to download it through the App Store, iMazing, or purchase history even though it may still show up there.
In this case, the easiest workaround is to add tiktok.com to your home screen and use it as a PWA app.