Asus made a crypto-mining motherboard that supports up to 20 GPUs - The Verge
Amazon.com: Biostar TB360-BTC D+ (Intel 8th and 9th Gen) LGA1151 SODIMM DDR4 8 GPU Support GPU Mining Motherboard. Requires CPU with IGFX and Server Power Supply. : Electronics
This crypto-mining Asus motherboard supports 20 GPUs, because 19 wasn't enough - CNET