The note taking app Bear supports integration via it’s Share extension, and URL schemes. For basic needs, use the Drafts Share action and select Bear in the iOS share sheet. Bear’s share extension supports capturing new notes, or append-prepending to existing notes you select in the share extension.
Bear has extensive x-callback-url support, allowing creation of new notes, as well as appending/prepending text, navigating to and searching notes. More details can be found in the Bear URL scheme documentation. A few ready-to-use example actions: