After running npm install -g expo-cli and successfully installing the packages globally, expo is still not recognized as an internal or external co
I may be too late to answer this, but for people looking for the same error this is what worked for me.
Install yarn if you don't have it. I used the command choco install yarn (you'll have to install Chocolatey). If you have scoop installed, scoop install yarn also works.
Use yarn to install expo with yarn global add expo-cli.
expo start should work now. yarn start and npm start should also work.
Hope that helps!