The 27-inch iMac 2019's RAM may be upgraded to 128GB - NotebookCheck.net News
Apple iMac 5K 27-inch (Mid 2019) 3.6GHz i9 8GB RAM 2TB SSD - Buy Refurbished iMac 2019 at Techable
Adamanta 64GB (2x32GB) 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
How to Upgrade iMac RAM: 2012-2022: EveryMac.com
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET