Downgrade Flutter 3.0 to 2.10 - May Not Be Needed

Likely, your app has an error about Warning: Operand of null-aware operation '!' has type 'SchedulerBinding' which excludes null.  

Probably, this error is in a package you are using and it is too much work to update the package you imported, so you're living with the error.  On Flame 1.1.1, I am ignoring this error.  It's possible that you can just ignore this error too.  However, if you want to go back down to Flutter 2.10.5 (latest stable) or Flutter 2.10.0 (version used in Flame examples as of May 17, 2020), then you go into your Flutter directory and run git checkout 2.10.0 or the version of Flutter you want to run.  Then, run flutter doctor.

If you do not know where your flutter is installed, you can also run flutter doctor -v