You should be able to upload files into App Inventor. Here are some simple steps. Try using Chrome or Firefox.
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I am stick to Chrome, so I can guarantee it works properly.
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Edge might have some errors I heard, but I never guaranteed it.
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Internet Explorer is unable to use MIT App Inventor.
Do note that the maximum file size you can upload is 5 MB. If you
I don't think so. Restart your computer or browser. It is working fine for me. What browser are you using?