iMac 21.5" Desktop - 3.0GHz Quad-Core i5 - 8GB RAM - 256GB SSD - (2017 – The Refurbished Apple Store
Crucial 16GB DDR4-2400 SODIMM Memory for Mac | CT16G4S24AM | Crucial.com
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