Crucial RAM 8GB DDR4 3200MHz CL22 (or 2933MHz or 2666MHz) Laptop Memory CT8G4SFRA32A at Amazon.com
Amazon.com: OWC 8GB (2 x 4GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S08P) : Everything Else