Upgrading an older iMac's PCIe SSD: Third-party solutions that save you beaucoup bucks
2013 iMac teardowns reveal SSD slots, soldered-in CPU in the 21.5” model | Ars Technica
iMac 2013 (and later) with NVME SSD? | MacRumors Forums
M Key NVMe PCIe M.2 SSD Adapter Card Expansion Card for 2013 2014 2015 2017 Macbook Air 27' imac 2013 2014 2015 2017|Computer Cables & Connectors| - AliExpress
SSD For Macbook AIR iMAC 2013 2017 NVME PCIE 2TB ssd for Mac|Internal Solid State Drives| - AliExpress
Fledging 256GB Feather M13-S PCIe NVMe Gen 3.0x4 SSD Upgrade – DIY kit & OS Included – Compatible with Apple MacBook Air (2013-2015) & Pro (2013-2016), Mac Mini (2013) & Pro (2014), iMac (2013-2019) | Pricepulse
Price history & Review on M key M.2 PCI-e NVMe SSD Adapter Card for MACBOOK Air Pro A1398 A1502 A1465 A1466 iMAC A1419 Mac mini 2013 2014 2015 2016 2017 | AliExpress Seller - COCO3C | Alitools.io
The OWC Aura Pro X2 SSD Review: An NVMe Upgrade For Older Macs
Upgrade/Install PCIe SSD in a 21.5-inch iMac(Late 2013)
The OWC Aura Pro X2 SSD Review: An NVMe Upgrade For Older Macs