iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
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 : Amazon.ca: Electronics
Memory Upgrades for iMac 21.5-Inch 2012 - Late 2013
Install memory in an iMac - Apple Support
How to Upgrade/Replace the Memory in a 21.5-inch iMac (2019) iMac19,2 - YouTube
Apple's New 21.5 Inch iMac Has Upgradeable Parts — That's a Huge Deal
How to Upgrade/Install Memory in a 21.5-inch iMac (Late 2012– Mid 2014) iMac14,1 iMac14,3 - YouTube
Apple's 4K 21.5-Inch iMac Allows You to Upgrade RAM and CPU – Company Finally Dialing Down on Soldered Components, Reveals Teardown
How to upgrade iMac (2020) RAM and save up to $2000 - 9to5Mac