OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
How to upgrade the RAM on the 27-Inch iMac (2020) | AppleInsider
How to Install Ram on the 2019 27 inch iMac and which Ram to Buy? - YouTube
Apple's 4K 21.5-Inch iMac Allows You to Upgrade RAM and CPU – Company Finally Dialing Down on Soldered Components, Reveals Teardown