The 27” iMac’s have always had socketed CPU’s. The 21.5” models low end models often had soldered CPU’s
But! You have been limited by the EFI to the CPU’s within the series . So in this case [https://everymac.com/ultimate-mac-lookup/?search_keywords=iMac19,1|iMac19,1 Series] CPU options.
The 27” iMac’s have always had socketed CPU’s.
But! You have been limited by the EFI to the CPU’s within the series . So in this case [https://everymac.com/ultimate-mac-lookup/?search_keywords=iMac19,1|iMac19,1 Series] CPU options.