Before AltStore and AltServer became the mainstream way of sideloading apps onto iPhones and iPads, you may recall using Saurik’s Cydia Impactor app. Unfortunately, the latter stopped working for users without paid Apple developer accounts some time ago.
Sideloady
Sideloady is a special app for macOS and Windows that allows users to sideload .ipa files on their iPhone, iPad, or Apple silicon-equipped Mac. These apps do not need to be installed via the App Store.