You won't be adding an aftermarket SSD to your new iMac | Ars Technica
Amazon.com: USB C 3.2 Gen2 MacBook SSD Enclosure for Apple Flash SSDs 12+16 PIN MacBook Pro MacBook Air Mac Pro iMac from 2013 to 2017, with Adapter to Support M.2 NVMe SSDs (
How-To: Now's the right time to swap your old iMac's hard drive for a fast new SSD - 9to5Mac
Upgrading a 27-inch iMac 5K to 14 terabytes - Replacing the Fusion Drive with both a SSD and an harddisk