I ran across this old article. Though the focus was for chestnuts the author mentioned this method having been used for apples and other woody cuttings. Unfortunately, I couldn’t find any updates.
If you search for “Buried In-arch Technique for Rooting Chestnut Cuttings” you’ll find the page to download a PDF of the article. (I don’t know how to copy the link to that).
Here’s a link to the book with the description: https://books.google.com/books?id=n_FJAAAAYAAJ&pg=RA3-PA24&lpg=RA3-PA24&dq=buried+in-arch+technique&source=bl&ots=TYRkthzSAz&sig=ACfU3U1Ubf0h4SAAmZh4eMC4sps2vJnDDw&hl=en&sa=X&ved=2ahUKEwjkh5b8y4DnAhUJCc0KHTGOAqoQ6AEwAnoECAoQAQ#v=onepage&q=buried%20in-arch%20technique&f=false
Has anyone ever tried this? It sounds like a good option for getting an apple or pear tree on its own roots, something that interests me. I’ve a number growing that were root or very low grafted and buried but it seems I won’t know down the line if the scion itself ever rooted or if it continued growing on the rootstock. Sue