> We need an open source alternative to https://www.princexml.com/samples/

TeXmacs: https://www.texmacs.org

As far as I know e.g. this book https://www.editions-ellipses.fr/accueil/4856-le-petit-pytho... has been written with TeXmacs, and antoher is in preparation by the same author. Also, Joris van der Hoeven has written a guide to TeXmacs ("The Jolly Writer") using TeXmacs