Android Studio sources don't have support classes. Decompiled .class file, bytecode version: # (Java #)

Can't read base Android classes from support library v 28. When I create a new project and click AppCompatActivity (Ctrl + click left mouse button) I see an error message: "Decompiled .class file, bytecode version: 51.0 (Java 7)" But when I open an Activity class, not from support lib, it opens normal. Also, if I change "implementation 'com.android.support:appcompat-v7:28.0.0'" in my dependencies to version 27.0.0 it works good. Seems, "Sources for Android 28" doesn't have support library by default. Can I install it manually? A year ago I saw a solution where I had to change some xml file to refer into the older version and it started work normal, but I can't find it now :(