When I press command+shift+p this pops up, instead of formatting.

That's expected. The popup you see is called the Command Palette.
When inside the command Command Palette you can search for Format Document as described in the usage section in the readme file.
You can define a shortcut yourself or use the built in formatter (also default). In my case it is shift + alt + f.

thanks so much!
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Most helpful comment
That's expected. The popup you see is called the
Command Palette.When inside the command
Command Paletteyou can search forFormat Documentas described in the usage section in the readme file.You can define a shortcut yourself or use the built in formatter (also default). In my case it is shift + alt + f.