Another solution for: Android Toast Message is not showing
As an absolute beginner in Android Studio I have not enough reputation to comment in the above thread, but for me this thread helped: The system ui isn't responding in android emulator (Flutter)
I found that thread on google, because always when I clicked a button, I got this message in the pixel 3a emulator after several seconds: "The system ui isn't responding". Instead of showing a Toast message. So I searched for this message and found that thread. After changing the "Emulated Performance - Graphics" from "Automatic" to "Hardware - GLES 2.0", the Toast message is showing. So I could solve two problems: Not showing Toast messages and and the problem with "The system ui isn't responding"
My Toast code: Toast.makeText(this, "This is a Toast message", Toast.LENGTH_SHORT).show()