Tablet Kindle books to PC Download/Transfer

I need a little help. While I don't own a Kindle, I have the kindle app of a tablet that I have some books on. After everything that's been going on recently I (tried) to backup what books I bought onto my PC, but it just won't let me. I know I'm doing something wrong but I don't know what.

From my computer on the amazon website, when I clicked on "download and transfer via USB" it says I don't have any compatible devices. So I tried to download the kindle app on my computer but it still said the same thing. Yeah, I know I'm dumb, but honestly I just buy physicals most of the time. I started doing ebooks recently because I just don't have the space for my books anymore and I don't want to get rid of them either, they're all precious to me.

If anyone knows what I might be doing wrong, that would be appreciated!