12GB OWC Memory Upgrade Kit (1 x 4GB + 1 x 8GB) 1600MHz PC3-12800 DDR3L SO-DIM | Megamac
OWC 32GB (2 x 16GB) PC21300 DDR4 2666MHz 260pin SO-DIMMs Memory Ram Module, Compatible with Mac Mini 2018, iMac 2019 and up, and Compatible PCs, (OWC2666DDR4S32P) at Amazon.com
How to Install Memory Into a 27-Inch Apple iMac (Late 2015 - 2020) iMac17,1 iMac18,3 iMac19,1 - YouTube
OWC Memory
OWC 128GB DDR4 2666 MHz SO DIMM 2019 iMac Compatible Memory Upgrade 4 x 32GB | eBay