I have installed Dart via the downloaded official SDK. Now, I would like to install it via the apt package. Therefore, I want to completely uninstall the SDK that I manually installed.
Since it was installed manually, neither of the methods to uninstall at the provided link work.
I have installed Dart via the downloaded official SDK
This installation method require you to manually download an archive and unpack the Dart SDK to a custom location of your own choice and add Dart manually to your PATH so it points to the location you have it installed.
So uninstalling just require you to do those steps in opposite. Yes, Dart will also save some generated data in your user folder but since you intend to install Dart again, it does not make sense to cleanup those data since they will also be used by the Dart installed though apt.