Apple iMac 27-inch (2019) review: Apple iMac 2019 is a millennial trapped in the body of a baby boomer - CNET
Install memory in an iMac - Apple Support
The 27-inch iMac 2019's RAM may be upgraded to 128GB - NotebookCheck.net News
Memory Upgrades for 2019-2020 iMac 27-Inch - Up to 128GB
Timetec 16GB Compatible for Apple DDR4 2666MHz for Mid 2020 iMac (20,1 / 20,2) / Mid 2019 iMac (19,1) 27-inch w/Retina 5K Display, Late 2018 Mac Mini (8,1) PC4-21333 / PC4-21300 SODIMM MAC RAM Upgrade at Amazon.com
Amazon.com: v-Color 128GB(4x32GB) 2666MHz ddr4 Compatible for iMac Retina 5K, 27-inch, 2019 and iMac Retina 5K, 27-inch, 2020 Non ecc SODIMM Mac Memory Ram Upgrade pc4-21300 CL19 260-pin 1.2V(TN416G26S819Q-VC) : Everything Else
OWC Announces RAM Upgrades for New 27-Inch 5K iMacs - MacRumors