How to Upgrade the Memory in the iMac Pro (late 2017) - YouTube
Amazon.com: OWC 32GB (2 x 16GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S32P) : Everything Else
64GB RAM upgrade kit for 21.5-inch iMAC now offered by OWC - 9to5Mac
Upgrade your iMac with OWC, 2017 4K Retina Edition | TweakTown
Install memory in an iMac - Apple Support
16GB Apple iMac 2017 21.5" Non-Retina RAM Upgrade iMac18,1