Your post made me want to check the rules of the "particule" in French [1], with regard to French names, as in: Charles de Gaulle, Jean de La Fontaine or Armand Jean du Plessis de Richelieu.
Turns out, capitalization depends on the grammatical construct. It's always capitalized at the beginning of a sentence, or to avoid ambiguity as in "Les mémoires de De Sèze". It's never capitalized when writing the full name (Jean de La Fontaine). In other constructs, it's complicated, and quite subjective...
Foreign names with particules follow the rules of the country of origin.
Turns out, capitalization depends on the grammatical construct. It's always capitalized at the beginning of a sentence, or to avoid ambiguity as in "Les mémoires de De Sèze". It's never capitalized when writing the full name (Jean de La Fontaine). In other constructs, it's complicated, and quite subjective...
Foreign names with particules follow the rules of the country of origin.
[1] https://fr.wikipedia.org/wiki/Particule_(onomastique)#Majusc...?