How to upgrade the 27-inch 5K iMac (2019) with a massive 128GB of RAM [Video] - 9to5Mac
Apple iMac 5K 27-inch (Mid 2019) 3.6GHz i9 64GB RAM 1TB SSD - Buy Refurbished iMac 2019 at Techable
OWC can double or quadruple the RAM in 27-inch iMac 5K | Cult of Mac
The 27-inch iMac 2019's RAM may be upgraded to 128GB - NotebookCheck.net News
Factory Original 64GB (2x32GB) Memory Upgrade for 2020 & 2019 Apple iMac 27" w/Retina 5K Display & 2018 Apple Mac Mini DDR4 2666Mhz PC4-21300 SODIMM 2Rx8 CL19 1.2v RAM Adamanta at Amazon.com
32GB (4 x 8GB) Memory Upgrade for 2019-2020 iMac (27-inch)