AltStore is the most stable tool for iOS 15. It uses your computer to refresh the app certificates automatically. Download and install on your Mac or Windows PC. Connect your iPhone or iPad to the computer via USB.
A tool to install the IPA (e.g., AltStore, Sideloadly, or 3uTools). Your Apple ID credentials. Step-by-Step Installation Process (Using AltStore): netflix ipa ios 15 new