OWC 32GB (2 x 16GB) PC21300 DDR4 2666MHz SO-DIMMs Memory, Compatible with Mac Mini 2018, iMac 2019 and up, and Compatible PCs, (OWC2666DDR4S32P) at Amazon.com
Compatible motherboards with Gigabyte 2666MHz DDR4 16GB (2x8GB) - Pangoly
128GB Memory Upgrade for 2019-2020 Apple iMac (27-Inch)