Hi @Vikas Kumar Singh ,
1,To enroll the existing Azure AD joined device to Intune, there are some methods without resetting the devices. Here is an article list the methods for your reference. You can choose one of them.
Intune MDM enrollment for devices already Azure Ad /Entra joined
2,For Hybrid Azure AD join devices, if you didn't want to affect the user, on my point of view, GPO enrollment can be a good option. It will do the enrollment in background automatically. As a reminder, please ensure all the login users has both Microsoft Intune license and Azure AD license assigned:
How to auto enroll a Hybrid Azure AD join device in Intune
Enroll a Windows device automatically using Group Policy
I know there are a lot of the devices needs to do enrollment. To ensure the project is doing smoothly, we suggest to firstly test on a few devices. If everything is working well on these devices. then we can do it on all the other devices.
Hope it can help. Have a nice day!
Best regards,
Simon
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