sd card reader

Have you done a PRAM reset, CMD+Option+p+r...

Reset NVRAM on your Mac - Apple Support

In fact, do 3 in a row, takes a bit of time.

Intel-based Macs: Resetting the System Management Controller (SMC)...

Reset the SMC of your Mac - Apple Support

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes or more.

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.

Does it show up innSystem Report>Hardware>Card Reader?

Have you tried different SD cards yet?

Does it show in Disk Utility?

Do other USB things work?

Good idea, & good luck my friend.