Apple 27-inch iMac (2019): No new ground, but welcome CPU and GPU upgrades | ZDNET
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
A-Tech 8GB RAM for Apple iMac 2017 (27 inch Retina 5K & 21.5 inch Retina 4K) | DDR4 2400MHz SODIMM PC4-19200 1.2V 260-Pin SO-DIMM Memory Upgrade Module at Amazon.com
Apple iMac 2020 5k Retina Display, Intel Core i5, 8GB RAM, 256GB SSD, 27 Inch, 3.1GHz, Silver MXWT2 in Dubai, Abu Dhabi, & Sharjah. - Shopkees UAE
OWC 32GB PC21300 DDR4 2666MHz SO-DIMM Memory Compatible with Mac Mini 2018, iMac 2019 and up, Dell, HP, Lenovo, ASUS and Compatible PCs (OWC2666DDR4S32G) at Amazon.com
The iMac G5's internals were obviously designed to be viewed by the user. It only takes 3 screws and 30 seconds to open it up. : r/apple