Origin of the Shield Shape in the Solar Folio of the f85-86 Foldout

[nablator]

Indeed, the point here is that four centuries later, in the early 15th century, the unknown scribes likely used elements of the Beneventan script to create the cipher.

Very unlikely. The U is not specifically Beneventan. The only similarity is the "re" that looks almost like k but the r is lower.