My Mac doesn't recognize SD cards

If a restart to your Mac doesn't change anything, there could be debris in the SD card slot. If you have an air compressor, you could blow to the slot at an angle.

It also could be that the Mac detects the SD card but there are no or damaged partitions so it fails to mount. For this, you could also try reformatting the SD card but this wipes the data in it: Erase and reformat a storage device in Disk Utility on Mac - Apple Support.

Is this a MacBook Pro that has a SD card slot on it or is through a SD card to USB adapter? Do any SD cards fail to be recognized?

Is there an error message that comes up or does the SD card just fail show up anywhere in the Finder or at the desktop?