解決：Could not get unknown property 'android' for project ':fluttertoast' of type org.gradle.api.Project

I had this problem with :path_provider & aapt2-proto and fix it in this way:

in project-folder/gradle/wrapper/gradle-wrapper.properties

change this:

distributionUrl=https\://services.gradle.org/distributions/gradle-5.6.2-all.zip

to this:

distributionUrl=https\://services.gradle.org/distributions/gradle-6.5-all.zip

and then in project-folder/buil.gradle

change this:

classpath 'com.android.tools.build:gradle:3.5.0'

to this:

classpath 'com.android.tools.build:gradle:4.1.1'

and then run this command

flutter clean

build or run your project, good luck.