This helped me, but the link (“read more about”) seems to have turned into something… unwanted and should be removed or updated. Here is a link to a snapshot of the source form the time of the post: https://web.archive.org/web/20210907035157/https://ownyourbits.com/2019/06/29/understanding-and-improving-nextcloud-previews/
The domain ownyourbits. com seems to be forwarded to some fishy abovenetwork. co.in domain.