Help! Plugged in SD card and photos not showing

I took the SD card out of my camera and plugged it in to the side of my MacBook (something I’ve done many times before). When I click on Nikon in the locations tab, the photos showed up for a moment and are now gone. Folder shows as empty.

I also went in to Photos library and tried to open from there and it says “no photos”.

When I try to eject the memory card it says “Disk Nikon wasn’t ejected because one or more programs may be using it. Don’t want to force eject in case that really deletes everything.

Any idea how to find out what program is using the disk?

Having a minor heart attack, hoping they’re not actually gone.