Is it true that centuries ago the Pope would not allow female choirs so they would castrate boys in order for them to reach high notes, the most famous of these being the Castrati singers?
Absolutely false.
While the Pope Sixtus V only allowed for a short time children who had this done there is no evidence or written proof to the church enforcing this on anyone.
This was actually more freely practiced in the aristocracy and arts of the time.
True or not I can see some people doing this on a voluntary basis. The fact that one pope allowed it can see others may not saying no to the practice but not openly supporting it either. I know some of the things the [Catholic] church has done can be very questionable when it comes to light.