Hi @IBN
Based on my knowledge, if the guest user could access Teams PowerShell to run the PowerShell normally, he can also access Teams admin center with no issue. From your description, we recommend you try to use InPrivate mode to login Teams admin center to see if this issue can be reproduced.
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Hi @IBN
Yes. you're right! I did a test in our environment and guest indeed have no permission to access Teams admin center.