Experience Tumblr Like Never Before
Not even just fanfics, this applies to literally any kind of media. Poetry, paintings, sculptures, graphite/charcoal drawings, pottery - if you like a post then LIKE IT.
I really don't understand how "without getting kudos or comments a fanfiction author is going to assume that people who clicked their fic didn't like it" became a controversial take.
I don't know why some people think an author should imagine, or guess that people who click their fic enjoyed it it when nobody is telling them that.
If you're re-reading a fic constantly, or leaving it up in your tab so that it re-loads every day for a hundred days the author is not going to know that unless you tell them. They'd love to hear it. It would make their day.
And if you don't tell them you liked their fic, there's no reason for them to assume you did.