Based on this:
https://everymac.com/systems/apple/imac/imac-aluminum-faq/imac-intel-aluminum-ho w-to-upgrade-hard-drive.html
It would appear that your system utilizes a SATA II interface.
Although, SATA III SSDs are "supposed" to be backward compatible,
it is not required by manufacturers to do so.
Therefor, you will want to verify with the manufacturer that it is
SATA II compatible. Even if it is, it does not necessarily mean it
will work in your Mac.
Macsales/OWC (Apple Mac Upgrades - RAM, SSD Flash, External Drives and More)
have tested their components in actual Macs for their compatibility and also have
all the tools and kits required to do the drive replacement, even if you don't use one
of their drives.