Chosen Solution

I want to buy a replacement Hard Drive for 2013 Apple iMac. I do not need a high capacity drive.

Here’s the IFIXIT guide to put it in iMac Intel 21.5" EMC 2638 Hard Drive Replacement and here’s IFIXIT’s upgrade kit iMac Intel 21.5" (Late 2012-2019) SSD Upgrade Kit While these are SSD’s Vs HDD’s I think they will meet your needs