You want to know what Microsoft license is required to scan Teams messages using the Office 365 Securlet.
As per Microsoft, a customer needs either one of the following licenses to scan MS Team messages:
Microsoft 365 E5
Microsoft 365 Compliance (E5/A5/F5/G5 Add-on)
Microsoft 365 Security & Compliance (F5 Add-on)
Microsoft 365 Information Protection and Governance (E5/A5/F5/G5 Add-on)