With the POP protocol the client downloads all messages that are found on the server that aren’t on the client. There isn’t really the concept of incremental downloads with that protocol. It may have been there before, but I believe that would have been a kludge.
POP isn’t a very robust protocol. See the second to last comment, by ByteHamster, in https://forum.k9mail.app/t/backing-up-email-to-usb-thumb-drive/3772 for a list of advantages of IMAP over POP.