en.wikipedia.org/wiki/Theodora_(senatrix)

The description "head of the papal chapel" does not match the office Theophylact actually held.

Theophylact is described in standard reference works as vestararius, an office tied to the papal treasury and temporal administration:

• Treccani explains that his title of vestararius meant "capo dell'amministrazione finanziaria della Santa Sede" — head of the Holy See’s financial administration.
• The New Catholic Encyclopedia says Formosus had appointed Theophylact vestararius, "an office of considerable influence and importance in the control of the temporalities of the Holy See."

So the office was connected with the papal court’s finances and temporal administration, not with being "head of the papal chapel."