Is there a way to mass enroll macs without sending an enrollment invite? like if jamf scans the network and finds 1000 macs. can they be enrolled automatically?

This used to be somewhat possible as long as you had a local admin account that you could use with Apple Remote Desktop or some other management app that could upload and remotely install packages. As of macOS 10.13.4, Apple introduced something called User Approved MDM. This means that an admin user logged into the Mac with access to the mouse and keyboard (not remote) must approve the MDM profile before it will be installed, and the Mac is enrolled. This is a security feature of macOS. No MDM solution can do this without the explicit approval of the user. Apple Business Manager allows for Macs to be auto-enrolled into and MDM server when they are first connected online and setup.