In Fieldmaps online I am creating a form and want the option to add a photo as an attachment. Just like in the iPhone picture in the top of this tutorial:
This tutorial however doesn't seem to show how to attach photos. Feel like I am missing something obvious.
That is set on the hosted feature layer, not in the form.
view item details for the Hosted Feature service, Overview Tab, select the Test Collection April23 layer, turn on attachments.
You will then be able to add attachments to features in Field Maps.
To expound on @RhettZufelt 's comments, once you enable attachments you will have the ability to take and attach photos in Field Maps mobile. It will be a big blue button and it does all the work for you.