After downloading any project, the extension is .sb2, it will not appear if I open it in my scratch app. because scratch app. only supports .sb extensions.
So I change it from .sb2 to .sb
After doing it and open it in the scratch app.
It says “Could not read project; file may be damaged: (bad header)”.

Please help!

You need to download and use the Download the Scratch 2 offline editor (beta version)

Oh. Thanks for your reply!