SD card won't open on iMac

Hello, can anyone advise on this please? I've just bought an iMac and a Ugreen adapter for SD card and USB flash memory. The Mac will show the adapter in Finder, but when I open the SD folder my film clips do not display. Nothing appears. However, the SD cards still work just fine on my MacBook. I have no problem with the flash drives on the adapter. I have, of course, tried all the ports. I am not sure where the problem lies. I'm not very technically minded.