The suggested numbers from ASUS website has only 3 configurations for the cards to reach the maximum number.Probably it is not updated but it is a good start to have a look there.The processor of that motherboard is an intel and as far as I know it supports up to gen 9 processor for the LGA 1151.The maximum you will go with a single vendor is 16 graphic cards because of the best processor i9 9900 supports 16 PCIEx lanes max.

Here is the link the official faq from ASUS : https://www.asus.com/support/FAQ/1034921