Hi, did you go through this https://video2.skills-academy.com/en-us/azure/azure-monitor/agents/azure-monitor-agent-migration
Once you onboard your VM to Arc you can install extensions, one of which would be MDE.windows, which is also the unified extension for Defender for Endpoint and Defender for Server.
You install extensions based on the service you want to use, MDE, Update Manager, Defender, Vulnerability Management, Assessments, etc etc
you can install extensions manually or through Azure Policies (DeployIfNotExist)
Alan