Purchase SSD for 2012 iMac running OS Catalina 10.15.7

if you want a drive that you are going to install internally into the Mac, I would recommend shopping at OWC. their main focus is Mac compatible hardware.

but if you want to use it as external storage, just about any external HDD or SSD will work. just make sure to not use any software that supposedly makes the drive "Mac ready". when you use software from just about any manufacturer for their storage device you run the risk of that same software not being compatible with macOS updates / upgrades. it can cause the software to stop working. at best this will cause you a headache. at worst it can render your data inaccessible. it is always best to use disk utility to erase and format a drive before use to remove any preloaded software.

please see Erase and reformat a storage device in Disk Utility on Mac - Apple Support

Call OWC's Customer Support and let them recommend the best external SSD for your particular Mac model, work needs and budget.

you're welcome. :)