looking for Mac 2021 compatible Micro-B to USB-C cable for external hardf rive

Your original post asked "looking for Mac 2021 compatible Micro-B to USB-C cable for Seagate external harddrive. Does this exist??"

A 2021 iMac 24" has USB-C ports. A USB-C cable will fit any of the ports on the back of either of the models shown below from iMac 24-inch - Technical Specifications - Apple

Two Thunderbolt / USB 4 ports with support for:

• DisplayPort
• Thunderbolt 3 (up to 40Gb/s)
• USB 4 (up to 40Gb/s)
• USB 3.1 Gen 2 (up to 10Gb/s)
• Thunderbolt 2, HDMI, DVI, and VGA supported using adapters (sold separately)

3.5 mm headphone jack

• Configurable with Gigabit Ethernet
• —

connections and expansion image for 2-port Model

Thunderbolt / USB 4

• Gigabit Ethernet
• Two USB 3 ports (up to 10Gb/s)

If they're compatible with A MacBook they're compatible with an iMac.

Also there are no special compatibility requirements for connecting a hard drive to a Mac.

You can either buy a new USB-C cable or if you have the old USB cable you can use it with an adapter such as USB-C to USB Adapter - Apple

or you can buy a USB-C to USB adapter from a 3rd party.

Amazon and other suppliers have many options. Do an internet search for usb0c to micro b.