How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
Timetec 8GB Compatible for Apple DDR4 2666MHz for Mid 2020 iMac (20,1 / 20,2) / Mid 2019 iMac (19,1) 27-inch w/Retina 5K Display, Late 2018 Mac Mini (8,1) PC4-21333 / PC4-21300 SODIMM MAC RAM Upgrade at Amazon.com
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET