sd card

In addition to resetting the SMC (Reset the SMC of your Mac - Apple Support) and NVARAM (Reset NVRAM on your Mac - Apple Support), be sure to read the troubleshooting steps in Use the SD and SDXC card slot on your Mac - Apple Support:

If your card doesn’t mount

If you insert your card and it doesn’t mount, remove the card and insert it again. Sometimes the SD card won’t mount properly if you insert the card too slowly or too quickly.

If the card still won't mount, you might need to reformat your SD card.

Personally, I've also found the SD card must be inserted quickly, otherwise it won't be recognized.

Jack

if it was me then I would test them with another computers

and test other SD cards with the imac to verify if the sd slot in the mac is defect or if the

sd cards were,

also I would check if they show up in disk ulity to make sure it's not the filesystem they were formatted in which was the culprit

This has been reported by others including myself. Try SMC and NVRM reset. Mine started working after I updated to latest version of Monterey OS.