Unable to open projects

[keith555]

I can't get any of the projects to open. They have multiple errors such as

import 'package:flutter/material.dart' - Target of URI does not exist.

There are many OmniSharp errors such as
Unable to resolve 'AutoMapper (>= 9.0.0)' for '.NETCoreApp,Version=v3.1'.

[newarjun101]

Check this <<<flutter doctor -v >>
I think because of SDK is unavailable

[keith555]

I'd already tried that. I've got some of the demos working by playing with the pubspec.yaml. I'm not sure exactly which change fixed the problem.