@Dheeman Das , Based on my test, I have deployed a shared multi-user profile assigned to an Azure AD joined device.
I try to remove the device group under assignment, add related user to the device primary user, restart the device. After performing sync, I find the guest account is not under the login screen. And then I login using an Azure AD account, after login, I find everything is working well. Not find any impact on this.
Before you do this to all the shared devices, to ensure nothing will be impact, you can choose some devices as test in your environment to check on this.
Hope it can help.
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