I enroll Chrome Browsers (via the enrollment key) into the OU the users are going to be in. The policies that apply are the Chrome user settings. This has nothing to do with ChromeOS device settings - so if you are trying to deploy them they won't do anything.
Its also important to set the precedence policy correctly. So do you want policies applied to users to trump browser policies or the other way round.
The typical use case for managed browsers is that when someone logs into Windows/MacOS, the browser automatically has the correct user policies applied and its not dependent on the user turning on sync.
As far as AD goes all you need to do is push the enrollment key and then set all your user policies in one place - the admin console. You can set the policy precedence to have the user policies take over if the user turned on sync if you have OUs of users within the OU where the browser is enrolled e.g. to push different custom bookmarks to the ones everyone gets perhaps.
My blog post on the subject from a while ago: https://wpsit.blogspot.com/2022/06/using-managed-browsers-with-google.html