Don't Upgrade The RAM In Your New Apple iMac, Do This Instead
A-Tech 16GB (2x8GB) RAM for Apple MacBook Pro (Early/Late 2011), iMac (Mid 2010 27 inch 4-Core, Mid 2011 21.5/27 inch), Mac Mini (Mid 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
Install memory in an iMac - Apple Support (HK)
Memory Upgrades for iMac w/ Retina 5K Display Late 2015
Install memory in an iMac - Apple Support (HK)
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
Amazon.com : Apple iMac MK482LL/A 27-Inch Retina 5K Display Desktop (Intel Quad-Core i5 3.3GHz, 8GB RAM),(Discontinued by Manufacturer) : Electronics
Install memory in an iMac - Apple Support
Apple Continues to Charge Hefty Premium for 2020 27-inch iMac RAM Upgrade - Third-Party Solutions
Install memory in an iMac - Apple Support (HK)
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com