NEMIX RAM 32GB Upgrade Kit (2x16GB) DDR4 2666MHz PC4-21300 SODIMM Memory Compatible for Apple iMac Mid 2020 iMac (20,1 / 20,2) / Mid 2019 iMac (19,1) 27-inch w/Retina 5K, Late 2018 Mac Mini (8,1) at Amazon.com
Memory Upgrades for iMac w/ Retina 5K Display Late 2015
How to upgrade the RAM on the 27-Inch iMac (2020) | AppleInsider
Amazon.com: OWC 32GB (2 x 16GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S32P) : Everything Else
Can you upgrade the RAM in the 27-inch iMac? | iMore