I can't run the emulator in Android studio, what's the problem?

Question

android studio

When you click on the RUN button, an error pops up:
This project uses AndroidX dependencies, but the 'android.useAndroidX' property is not enabled.


I found a solution (or not a solution) on the Internet, put the code in the gradle.properties file:

android.useAndroidX=true
android.enableJetifier=true

But now another error pops up:
error: cannot find symbol import android.support.v4.app.Fragment;


How to solve this problem?