On the origin of the Spanish Ñ

Where does the Spanish "Ñ" come from?
We all know that monks in the Middle Ages, working in their Scriptoriums (or scriptoria), where one of them recited aloud and the others copied, used shortcuts to speed up the process of copying. The most famous is the Spanish “Ñ”. The double n (nn) in Latin, annus, for example, was shortened by writing only one “n” and placing the diacritic tilde on top, to indicate the absence of an “n”, adding thus a letter to the Spanish alphabet, and turning annus into “año”. This practice we will find in French, Portuguese and German, to mention only three other languages.
(I refer the reader to my article in VivaFifty (April 8, 2019) "Is textese poor spelling and bad grammar?" where you will find more info.)