External floppy drive for iMac

That's going to depend on the type of floppy and how it's formatted.

A current run of the mill USB floppy drive should allow you to read most regular 1.4Mb floppies without issue.

400K and 800K Macintosh formatted floppies are no longer supported and an older Mac will be required.

click here ➜ USB Floppy Drive - Amazon.com

You won't be able to read the floppy disc because the last system that could was Mojave, 10.14. So you would need an older Mac running Mojave or earlier and a floppy disk drive to be able to read/recover the files on the floppy disk.

Assuming those floppy disks are even still intact. I know some of my old floppy disks have deteriorated over time & became unreadable.

Assuming the floppy disks are for a standard 1.4MB floppy, then you may be able to access them using a Linux system which would either require a 2015 or earlier Mac, or a standard Windows PC booting a Linux OS....a bootable Knoppix USB stick may be sufficient since it includes lots of drivers installed by default and does not require touching the internal boot drive of a Mac or Windows PC (may require use of the command line though).

Back in late 1999, I purchased a SmartDisk VST 1.44 MB Floppy disk drive for my iMac DV SE. Here is an image of a diskette presently mounted to my macOS Tahoe 26.1 Desktop on my M4 Mac Mini Pro:

This is connected to my 5-port USB-C StarTech hub using a USB to USB-C dongle.