There are many libraries I use every day from pub and they work. But today I run into a problem with qr_code_scanner. After installing it with flutter pub add qr_code_scanner and running flutter pub get, I get in code:
Same with auto import for classes from this file like QRViewController. What I also did is running flutter upgrade, flutter clean and everything else that came to my mind - still getting this error with that package.
Any other thoughts how can I solve it?

Some of the packages you are using are upgraded to flutter3 and some are still Flutter version < 3. Which is why you might be facing an issue. If you are trying to build an older project I would recommend you to downgrade your package versions which is compatible with flutter < 3 and use flutter version < 3. If you are adding any packages through pub add you might get an error if the pub get is not resolved. Please check the same in terminal.