@Pankaj Lohumi Azure AD Premium P2 license is assigned on per user basis. If only 100 users wants to use the premium features, license needs to be assigned to only those 100 users and not to all 200 users.
For guest users, you need to maintain 5:1 which means, if guest users want to use Premium P2 features, you don't need to assign 5 licenses to 5 guest users. You just need to assign 1 license to any of those 5 guest users. If 10 guest users want to use Premium feature, assign license to only 2 guest users out of those 10 users, in order to stay compliant.
Hope this answers your question.
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