If you have already the users in Groups, I would go to assign the policies to Groups bearing in mind the precedence mechanism that Teams uses when policies are assigned: https://docs.microsoft.com/en-us/microsoftteams/assign-policies?WT.mc_id=M365-MVP-4015732. On the other hand, assigning policies through Groups does not mean you cannot use PowerShell for that assignment, in did you can use it
I am always happy to answer a question I am mentioned in after the questioner has searched to see if I have written about the topic. In this case, you could search for "teams bulk assignment tony Redmond" and then ask if you don't understand something I said.
I noticed you @mentioned my previous account. For the record you cannot assign Teams policies to guest users. You can only configure the Org-wide -> Guest access settings. You can determine how meetings deal with anonymous or external users, for example, but not assign the policies directly to the external users. It's simply not supported.
If you have already the users in Groups, I would go to assign the policies to Groups bearing in mind the precedence mechanism that Teams uses when policies are assigned: https://docs.microsoft.com/en-us/microsoftteams/assign-policies?WT.mc_id=M365-MVP-4015732. On the other hand, assigning policies through Groups does not mean you cannot use PowerShell for that assignment, in did you can use it
