@Takahiro Watabe(渡部貴大), Thanks for posting in Q&A. Based as I know, for Intune, we can set conditional access policy to only allow authorized devices to access your organization's resources.
https://learn.microsoft.com/en-us/mem/intune/protect/conditional-access
https://learn.microsoft.com/en-us/mem/intune/protect/device-protect
But if you want to block unauthorized devices to access your network. I think Intune can't do this. You can contact network product with Internet traffic monitoring function to see if they can do this.
Hope the above information.
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