@Gokul R Dev, Thanks for posting in Q&A. From your description, I know the devices are all Azure AD joined. But the Startup Performance still shows boot time slow with Group Policy on some devices. if there's any misunderstanding, feel free to let us know.
In fact, Group Policy analytics is a tool to check if the on-premises GPOs setting have a replace in Intune when we migrate GPO setting to the setting in Intune. But as I know, we don't have on-premise AD environment. So we don't have to do the migration and no need to use this tool.
To check on our issue, I have done researching more, I find the total boot score is collected based on all device objects reported Boot performance data on the tenant. All the metric values are the current tenants averages and are compared with the averaged Boot time data. Based on the above average boot times, current tenant's Core boot score and Core sign-in score are computed using a linear mapping table derived from commercial median boot times.
Also around the Group Policy time slowness, from report side Any device which takes more than 1 second for group policy would be considered to be slow. Currently from admin side there is no option to reset this threshold for GP process time. As we don't have on-premise GPOs from DC,the group policy we can get is only from local group policy. Please check if any group policy is set on the device side locally. If not, we can ignore this.
Meanwhile, you can try to feedback to Intune uservoice to see if we can change this feature behavior.
https://feedbackportal.microsoft.com/feedback/forum/ef1d6d38-fd1b-ec11-b6e7-0022481f8472
Thanks for your understanding.
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