I’m trying to scan a set of documents using my Notes app, but I can’t find a camera icon on my Notes app

To add a photo or video, tap in a note, then tap the Camera button. Tap Take Photo or Video to create a new photo or video, or Choose Photo or Video to add an existing one. Tap Use Photo or Use Video, or tap Add to add an existing one. You can also scan documents and add them to your notes.

More information: Use Notes on your iPhone, iPad and iPod touch – Apple Support (UK)