The biggest difference between the Huawei P40 Pro and the more expensive P40 Pro Plus are the phones' telephoto lenses, as the P40 Pro Plus offers a 10x zoom lens versus the P40 Pro's 5x zoom. Apparently, though, there's also another distinction: the two phones sport displays made by different companies.
https://www.notebookcheck.net/Huawei-may-have-reserved-the-best-displays-for-the-P40-Pro-Plus-pre-orders-begin-in-China.467543.0.html