GrapheneOS 2021.04.22.20 release: grapheneos.org/releases#2021..
See the linked release notes for an overview of the changes since the previous release.
Conversation
The build instructions include the emulator target:
grapheneos.org/build
It won't have a proper up-to-date hardened kernel or the hardware-based security features, but you can test a lot of things there. It isn't meant for anything more than development at the time being.