How to open an older external HD

Within Disk Utility click "View" and select "Show All Devices" so that the physical drives appear on the left pane of Disk Utility. If you still don't see the physical drive, then you have a hardware issue of some sort. It could be the drive, or it could be the cable, or adapter.

If you see the physical drive within Disk Utility using the method I described, then we may be able to assist you in getting access to the data on that drive.

If an external hard disk drive does not appear in Disk Utility, it might as well not exist, as far as the Mac is concerned. The usual troubleshooting steps include substituting another connection cable, a different power supply (if the HDD uses an external power supply), a different port, a different Mac... etc.

Try booting Recovery mode and using its version of Disk Utility: Use macOS Recovery on a Mac with Apple silicon - Apple Support

What is that device's exact model designation? The hard disk drive itself may be ok, but its enclosure (meaning, its communication interface and related support electronics) may have failed. In that case the hard disk can often be removed and installed in a different enclosure. Some enclosures have different ports you can try.

Let us know what you determine.

Does it appear in Disk Utility?

Disk Utility User Guide for Mac - Apple Support

Connect and use other storage devices with Mac - Apple Support

See the devices connected to your Mac - Apple Support