How To: Upgrade 2017 5k iMac RAM to 64GB & Saved $840 | 2018 - YouTube
Memory upgrade: Apple iMac 2012/2013/2014 (Howto)
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