You can see the memory options at this OWC page. Finding a link to the DIY instructions is a little convoluted, but go here and click the one that specifies memory.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365