How do I disable the purple highlighting of search results within the content of a note?

Since you don't notice the problem, I suggest you do a small test. Create a new note and name it, for example, "company." In the content of this note, enter about 20-30 email addresses with the @company.com domain. Then go back to the search bar, type the first three letters "com," and see how the note looks. It is completely unreadable and makes work difficult.