In the past, the Android Emulator is always a standalone nice Emulator not attached to Android Studio. It is very helpful for a quick snapshot for documentation purpose, as it looks like a real device without the Window Frame.
However, after installing Android Studio Dolphin, the Emulator either Dock to the Android Studio or having an ugly Window Frame around it as below.
Can I get rid of the Window Frame?
You can't get rid of the window border, because they added the feature to include the emulator inside Android Studio (Refer to the Emulator patch notes 30.0.10).
If it is unbearable, then there is the option to run the emulator from the command line as instructed here. But you have to run your app in Android Studio beforehand.
Personally I would just deal with it. Taking screenshots is still possible with the menu points on top. But other than that I couldn't find another option.
Update: I actually found the setting to remove the tool window and just get the emulator as a floating window.
In Android Studio, go to the Settings, search for "Emulator" (its in the secion "Tools" and untick "Launch in a tool window".
Hope this is the answer you are looking for