Upgrading an older iMac's PCIe SSD: Third-party solutions that save you beaucoup bucks
Amazon.com: Timetec 256GB MAC SSD NVMe PCIe Gen3x4 3D NAND TLC Read Up to 1,950MB/s Compatible with Apple MacBook Air (2013-2015, 2017), MacBook Pro (2013-2015), iMac (2013-2019), Mac Pro (2013), Mac Mini (2014) : Electronics
How to Install/Upgrade the PCIe SSD in a 27-inch iMac (Late 2014 - Mid 2015) on Vimeo