You don’t need a third-party app to take a scrolling screenshot on an iPhone with iOS 14 or later.
1. On your iPhone, go to the page you want to take a long screenshot of.
2. To take a screenshot on your iPhone, press the power button and the volume up button at the same time.
3. Touch the floating thumbnail in the lower left corner of the screenshot.
4. Click the Full Page tab to take a picture of a scrolling page.
5. If you get the results you want, tap “Done” in the upper right corner and choose “Save PDF to Files.” The Files app is where your iPhone’s files will go.