tldr: copying or export from the project level will combine the notes within that project to the clipboard or a file.
I have been wishing for some slightly more outliner-ish behavior; I work with transcribed interviews a lot and end up with notes with >5000 words pretty often. I decided to try adding another level of hierarchy to my system, and to split what had been 1 note into 4 separate notes in a separate project, so I could collapse or show the different sections independently.
This works very well for me, but it leaves me with 4 notes at the end of each project instead of one…and normally I would make a Markdown archive of my finished note and file it in DevonThink. I couldn’t figure out a way to combine the notes easily (on iOS), until I realized that you can export AN ENTIRE PROJECT as a single note! If you select the “…” menu for a given project, the options for “Copy as” and “Export” will combine all notes within the project into the format you specify. It even puts a separator (‘—‘) between the notes for the Markdown export.
This turns out to be exactly what I need, and tbh feels like what is probably an intended workflow that I didn’t immediately understand because of thinking about the app in a more traditional way.
Posting so that other folks may stumble on this functionality a little easier!