@PKP,Thanks for posting in Q&A.
To create group, there are two types we can choose:
Assigned groups - Manually add users or devices into a static group.
Dynamic groups (Requires Azure AD Premium) - Automatically add users or devices to user groups or device groups based on an expression you create.
https://learn.microsoft.com/en-us/mem/intune/fundamentals/groups-add
To automatically add devices to groups, you can create rule to do this. Currently, there's no rule with percentage. But you can check if there's any property like deviceModel or others can accomplish your requirement. Here is a link with more details for the reference:
https://learn.microsoft.com/en-us/azure/active-directory/enterprise-users/groups-dynamic-membership
Hope it can help.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.