After upgrading to Android Studio 4.1.3 on macOS, the Android Emulator stopped working because the IOUSBHost library was missing. This issue affects macOS Mojave and earlier. When you try to launch an AVD, you may see the error: "The emulator process for AVD was killed."
A bug report has been created for this issue. If you have upgraded and encountered this problem, please let the developers know using the link above.
If you don't have time to wait for a fix and don't have a physical device for testing, your only option is to downgrade, as described here.
UPD 2021-04-02: Fixed in Android Emulator 30.5.4.