It's in the PEN list of books that are being or have been banned in various parts of the USA this decade (I think it's only this decade). It's banned from classrooms in Central York, Pennsylvania since September 2021.
docs.google.com/spreadsheets/d/1hTs_PB7KuTMBtNMESFEGuK-0abzhNxVv4tgpI5-iKe8/edit#gid=1623346099
sorted by author and title. In that, it's number 286 out of 1587.
I too would like to know why it's banned there, but I think my best guess must just be what I wrote above; I can't find anything more either.
It's in some pretty good company, though: A Wrinkle in Time was banned from classrooms for a while in some places too, and Flowers for Algernon, and Black Beauty, and Green Eggs and Ham.
(I can't find reasons for any of them.)