2013 iMac teardowns reveal SSD slots, soldered-in CPU in the 21.5” model | Ars Technica
Amazon.com: Sintech M.2 nVME SSD Adapter Card Upgrade Kits,Compatible for MacBook Air(2013-2017 Year) and MacBook PRO(Late 2013-2015 Year,iMac : Electronics
iMac Late 2013のSSDを換装してみた話(備忘録) – あの角を曲がれば、かぼしー
iMac 2013 (and later) with NVME SSD? | MacRumors Forums
Apple iMac 21.5” SSD Upgrade (2013-2015) HDD To Solid State Drive (SATA) | Step By Step - YouTube
I got a FREE 2013 iMac 21.5 with internal upgrades including Samsung evo ssd and 16gigs of ram. Then used open legacy patcher to install Mac OS Venture 13.5 beta. : r/osx