Don't Upgrade The RAM In Your New Apple iMac, Do This Instead
A-Tech 32GB Kit (4x8GB) RAM for Apple iMac (Late 2012, Late 2013, Late 2014, Mid 2015) | DDR3 1600MHz SODIMM PC3-12800 204-Pin SO-DIMM Max Memory Upgrade at Amazon.com
Apple 27" iMac with Retina 5K Display (Mid 2017) Z0TR-MNED43-BH
Memory Upgrades for 2019-2020 iMac 27-Inch - Up to 128GB
Install memory in an iMac - Apple Support
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com