I scraped metadata from AO3 using a homemade script, parsed it with the BeautifulSoup python package and made the plots in matplotlib and seaborn. I included all works returned by AO3 when I click on the tag "The Old Guard (Movie 2020)", i.e.: 'https://archiveofourown.org/tags/The%20Old%20Guard%20(Movie%202020)/works' on 17 August 2020. This tag has been wrangled, so it also includes works tagged "The Old Guard (2020 Movie)". I didn't apply any other filters.
I was not logged in to AO3, so this analysis does not include any works that are visible only to logged-in users.