2017 Apple iMac with Intel Core i5 (21.5-inch, 8GB RAM, 1TB Storage) - Silver (Renewed)
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 Retina 5K: Memory upgrade (RAM)
A-Tech 32GB (2x16GB) RAM for Apple iMac 2017 (27 inch Retina 5K & 21.5 inch
How To: Upgrade 2017 5k iMac RAM to 64GB & Saved $840 | 2018 - YouTube