command not found: create-react-app
Open Terminal
Go to c:/users and run dir /x
check shorter name of your usernsme you found with dir/x
//In my case my username is Nandini Jain and I got short id= NANDIN~1
and run npm config set cache "C:/Users/<shortname-you-found-with-dir/x>/AppData/Roaming/npm-cache" --global
//I ran the command
//C:/Users/NANDIN~1/AppData/Roaming/npm-cache" --global
now run
npx create-react-app my-app
//HOPE THIS WILL WORK BECAUSE ITS THE ONLY REASON OF YOUR QUERY.