I wanted to move some photos from my camera’s USB card to my new Macbook (M1, Big Sur). I connected a USB card reader to one of the Mac’s ports using an adapter. Finder did not see the card. Odd, because when I then removed the card, it gave the usual warning about not pulling out disks before unmounting them first. Using Diks Utility I found out that the Mac does indeed see the card reader and card, it just doesn’t show them in Finder. The likely reason is that card has no name. On my previous laptop the machine would simply list the card as ‘NONAME’, but apparantly not on this machine.
Right clicking on the card in Disk Utility and selecting ‘rename’ allows you to set a name. After that, throw out the card from the machine, remove it from the card reader and then put it back in. Et voila, the card is listed in Finder with its new name.