While reading all your wonderful responses to my question, https://bookstodon.com/@anderlandbooks/112269285790999076
I remembered that I do have a professor for medieval studies in my acquaintance, who is a native German but teaches in England. Here is her response, in case any of you ever face a similar problem (translation in alt).
I wasn't aware that Sir only came to England with the Normans in the 11th century and is based in French. #wordweavers#writerscoffeeclub#pennedpossibilities#writerscommunity
Firlefanz