Unable to save textedit to sd card

This is a MacBook Air with macOS Monterey 12.7.6.

I wrote a paper in TextEdit and saved to an SD card years ago.

I pulled it up and started making some changes. The first time I saved the changes it seemed to work. Then when I make another change and go to 'save' I get this message 'The document 'Book.txt' could not be saved. The file is Locked. Do you want to save your changes to it anyway? I click 'Yes save changes". Then I get this message. "You don't have permission to save the file 'Book.Txt' in the folder 'Book.Txt'. To new or change permission select the item in the Finder and choose Files> Get Info. When I save anyway it makes a new file with nothing in it.

I go to the 'Get Info' and find 'Sharing and Permissions'. I am unable to open it.

I changed the TextEdit to Rtf this made no difference.

Have tried asking Help. But, that is No help at all. I tried saving to a new SD card. No luck.

Can anybody help?