Why are my SD cards showing the wrong memory?

For a few years I have inserted SD cards into the appropriate slot on my iMac and downloaded trail camera videos from various cameras. Over the past 2 weeks, none of the cards now show the accurate disk space on the card. This is not a situation of me forgetting to delete files from the trash or anything like that.

The numbers don't make sense either. A 32gb card will say 45 gb free and 17gb in use.

If I "get info" on the card, it will have a certain capacity and then note that a bunch of the space is purgeable. I'm confused.

Why did this just start? Is there a way to reverse this so that the memory reflects accurately again?

Thank you.