try these steps :-

1. check the flutter is installed successfully (Flutter Doctor).
2. update Vscode and flutter sdk.
3. Run Dart Analysis Server in a Separate Terminal. open the terminal and past this command dart --enable-asserts --observe --pause-isolates-on-exceptions=always --no-sound-null-safety /path/to/your/project/lib/main.dart

if any of these steps not worked please send the ss of go to output (when the error occure their is a blue box)