Surprise! The iMac Pro has Upgradable RAM and SSD - The Mac Observer
2017 iMac SSD upgrade & Speedtest - YouTube
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Amazon.com: Odyson - 256GB SSD (PCIe 3.0 x4, NVMe) Replacement for Apple iMac (2017-2019) : Electronics
iMac Pro Base Model Teardown Reveals 2x SSD RAID Configuration and Four 8GB DIMM Modules - MacRumors
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 (
Upgrade your iMac with OWC, 2017 4K Retina Edition
iMac 5K - 4790K, M295X - thermal compound + second SSD upgrade + Air Vents MOD | MacRumors Forums