I work mainly with undocumented stuff. That taught me to appreciate when there is manuals and documentation for anything and I read them. I don't watch YouTube videos, I read the manual. Of course until I can't figure it out and then still look into YouTube anyway.
Exploring the UI is a perfectly valid method of discovering functionality. What’s the alternative? The phone interrupting you every 2 steps saying hey by the way, you can also do this and this from here?
Clicking on a kebab and getting a clearly-labeled “scan document” option seems like an eminently followable clue. It’s not like it’s a minuscule inscrutable icon three levels down.
You can get it through Books or on the web:
https://support.apple.com/en-gb/guide/iphone/iphf2746307f/18...