You can add apps to your Apple Watch directly through the Watch's App Store, or through your iPhone's Watch app.
You'll have to go into your settings to trust non-App Store apps on an iPhone. Here's how to make your iPhone trust these ...
Apple is officially letting third-party app stores for iPhones in the EU, starting with iOS 17.4. Developers can create alternative app stores for iPhones and offer different apps and services outside ...