@Kavindu Dayananda , For the users with device administrators role, they become local machine administrators on all Windows 10 devices that are joined to Azure Active Directory. From your description, it seems the devices are Hybrid Azure AD device. Based on my research, it is not suitable for Hybrid Azure AD joining devices. We can see more details in the following link:
https://dirteam.com/sander/2020/08/31/knowledgebase-the-device-administrator-role-is-not-available-on-the-roles-and-administrators-pane-in-the-azure-portal/
Note: Non-microsoft link, just for the reference.
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