The 27-inch iMac 2019's RAM may be upgraded to 128GB - NotebookCheck.net News
How to upgrade the 27-inch 5K iMac (2019) with a massive 128GB of RAM [Video] - 9to5Mac
Adamanta 32GB (2x16GB) Memory Upgrade for 2020 Apple iMac 27" w/Retina 5K Display, 2019 Apple iMac 27" w/Retina 5K Display, 2018 Apple Mac Mini DDR4 2666Mhz PC4-21300 SODIMM 2Rx8 CL19 1.2v DRAM
Memory Upgrades for 2019-2020 iMac 27-Inch - Up to 128GB
How to: 27-inch 5K iMac (2019) 128GB RAM Upgrade - Save $$$! - YouTube