Factory Original 64GB (2x32GB) Memory Upgrade for 2020 & 2019 Apple iMac 27" w/Retina 5K Display & 2018 Apple Mac Mini DDR4 2666Mhz PC4-21300 SODIMM 2Rx8 CL19 1.2v RAM Adamanta at Amazon.com
Install memory in an iMac - Apple Support
How to: 27-inch 5K iMac (2019) 128GB RAM Upgrade - Save $$$! - YouTube
Amazon.com: A-Tech 128GB Kit (4x32GB) RAM for Apple iMac 2019 & 2020 27 inch Retina 5K | DDR4 2666 MHz SODIMM PC4-21300 / PC4-21333 260-Pin SO-DIMM Max Memory Upgrade : Electronics
2017 21.5-inch 4K iMac memory upgrade kit includes 32GB of RAM, tools to take it apart | AppleInsider
v-Color 32GB(2x16GB) 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 (TN416G26D819K-VC)
Apple iMac 2019 (Early) 21.5-inch (Retina 4k) OSX , Ram & SSD Upgrades - ZD Laptop Service Centre
Memory Upgrades for 2019-2020 iMac 27-Inch - Up to 128GB