How to Install Safari Extensions in iOS 15:
1.Launch the Settings app on your iPhone and scroll down to Safari.
2. Now, choose the “Extensions” options and tap on “More Extensions“.
3. After that, explore the Safari extensions available on the App Store and download your favorite ones.
Alternately, you can also launch the App Store on your iPhone or iPad. Then, search for “Safari extensions”, pick the one you like, and install it like any other app.