Microsoft recommends adding the Microsoft Defender for Endpoint onboarding script to the AVD golden image. This way, you can be sure that this onboarding script runs immediately at first boot. It's executed as a startup script at first boot on all the AVD machines that are provisioned from the AVD golden image. However, if you're using one of the gallery images without modification, place the script in a shared location and call it from either local or domain group policy.