With the recent Flutter stable release, it was announced that IDE support for SDKs prior to 3.13 is deprecated:

https://medium.com/flutter/whats-new-in-flutter-3-35-c58ef72e3766

With this release, we are deprecating IDE support for Flutter SDKs before 3.13.

Flutter 3.13 / Dart 3.1 (shipped August 2023, a little over two years ago) will become the new minimum version.

For the upcoming release, we will mark these as "unsupported soon" so that prompts are shown to anyone still using these versions, and in a subsequent release they will be marked as "unsupported now".