Errors related to lack of support java 8 despite Retrolambda

Question

I followed this readme https://github.com/evant/gradle-retrolambda

I added classpath 'me.tatarka:gradle-retrolambda:3.7.1' to gradle.build

and

apply plugin: 'me.tatarka.retrolambda' to gradle.build (app)

and

android {
compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

But I'm getting error like:

Invoke-customs are only supported starting with Android O (--min-api 26)
Default interface methods are only supported starting with Android N (--min-api 24): Landroidx/room/migration/AutoMigrationCallback;onPostMigrate(Landroidx/sqlite/db/SupportSQLiteDatabase;)V