4 stars is too high a bar. There are plenty of books that receive 4.5 stars that I rate as 3, and occasionally 2. Of course there is a correlation, but it's weak. A lot of the old Reddit darlings (probably now also Lemmy darlings) are a bit meh for me, and so conversely, a lot of less popular books are good for me.
I think I wouldn't go below 3 stars on rating sites like Goodreads/storygraph. That's where the correlation seems to make it make sense. The current book i haven't read for several days because it sucks is rated 3.6...