iMac Intel 21.5" Retina 4K Display (2017) RAM and SATA Hard Drive Upgrade - iFixit Repair Guide
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
iMac 21.5" A1418 - Mid 2017 • Beetstech
Apple iMac (27-inch, 2017) review: Apple doesn't mess with success - CNET