This issue with SD slots has been discussed a few times on this forum.
But 8 times out of 10, the culprit is a tiny plastic "fin" that has broken off one of your cards and wedged itself into the card locking mechanism.
Getting a good look at it can be tricky, especially if the plastic bit is camouflaged black. If you're lucky it broke off one of your bright orange cards.
But if you can see if there's a bit stuck in there, and you have the dexterity and a fine enough tool, you might be able to pry it out.
But if you get too vigorous, you can mangle the entire mechanism. The best way to deal with it is to get a repair tech to remove the board from the camera and work with it that way.