I see a grey X next to my Windows files and they can't be opened after disabling computer backup

Hello! I used to use the backup feature of Dropbox for my computer. Notably, this included my Documents folder (on Windows 10). At some point I turned off the backup feature because I thought I didn't need it any more. I thought this would stop the integration with my computer gracefully, but it seems that now many of my files in my Documents folder are no longer accessible, as if they were made online-only (but there is no longer an online version backing them). Some screenshots attached. The problem files appear with a grey X on the bottom left of the icon. If I try to open them, I get failure and an error message sometimes depending on the program trying to open it. I do not have OneDrive, which is the usual cause I see online for the grey Xs.

How can I get my files working again?

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