Late 2013 iMac updated to Sonoma - runs absolutely fine. : r/OpenCoreLegacyPatcher
Amazon.com: Odyson - 1TB SSD Replacement for Apple MacBook Pro 13" A1502, 15" A1398, Replacement for Apple Mac Pro A1481, 21.5" A1418, 27" A1419 (Late 2013-Late 2014) : Electronics
2013 iMac teardowns reveal SSD slots, soldered-in CPU in the 21.5” model | Ars Technica
NEW Apple SSD Upgrade 2TB For MacBook Pro Retina 13" 15" 2012 2013 A1425 A1398 | eBay
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