The customizer worked great for almost everything. However, although I checked to disable the Sheet/Event Title Header (title-header) in multiple locations, it was not removed from the “Sheet Details” page.
I’m guessing you are confused about what the Title Header actually is, as it may not be completely obvious unless you look at what the default is, which is “Title”.
That’s when you have a list of sheets, it’s the text for the column header of the table column that shows the title of the sheet. The default “header” for that column is “Title”. But, you can use the customizer to change that text to anything else you want, or, if you check the box to remove it, that column header will be blank.
That column is not used on the sheet details page, so that option has no effect when you are viewing that page.
That Title Header has nothing to do with page titles or sheet titles.