Hello, Richard Bailey3.
Thank you for using Apple Support Communities.
From your post, we understand you're unable to use some photos stored in the Files app. We'd be glad to help. Apps would need permission in order to access content within the Files app. Currently, Photos and Twitter do not have the option to access Files. To see what apps have access, go to Settings > Privacy > Files and Folders.
About privacy and Location Services in iOS and iPadOS
"Privacy settings in iOS and iPadOS help give you control over which apps have access to information stored on your device."
You'll need to save the images to photos in order for them to be shared with other apps or to be edited. To send the JPEGs and PNGs to Photos, go to the Files app and tap on the file. From there the bottom left corner has this icon, tap on this icon and at the bottom should be an option to save image. This would add it to your photos and can be edited or shared from there.
Let us know if this helps.
Cheers!