For flutter version 3.x.x

File for minSdkVersion to change is

/flutter/packages/flutter_tools/gradle/src/main/groovy.flutter.groovy

Change minSdkVersion to at least 21.

/** Sets the compileSdkVersion used by default in Flutter app projects. */
    static int compileSdkVersion = 33

/** Sets the minSdkVersion used by default in Flutter app projects. */
    static int minSdkVersion = 21

/** Sets the targetSdkVersion used by default in Flutter app projects. */
    static int targetSdkVersion = 33

For flutter version 3.x.x on MacBook M series chips,

File for minSdkVersion to change is

/flutter/packages/flutter_tools/gradle/src/main/groovy.flutter.groovy

• Change minSdkVersion to at least 21.
• Currently, compileSdkVersion should be at least 35

/** Sets the compileSdkVersion used by default in Flutter app projects. */
    static int compileSdkVersion = 35

/** Sets the minSdkVersion used by default in Flutter app projects. */
    static int minSdkVersion = 21

/** Sets the targetSdkVersion used by default in Flutter app projects. */
    static int targetSdkVersion = 35