SendGuard is not prompting even after assigning licenses to users

If users cannot see or use SendGuard even though you’ve manually assigned licenses, it usually means the software hasn’t been fully installed or deployed. You may also notice a red exclamation mark next to the users’ email addresses in the Manage Users section of the SendGuard Management Console.

This happens because SendGuard requires two steps to be completed:

A red exclamation mark indicates that the license is assigned but the software is not yet installed. This could be because deployment hasn’t been done, or Microsoft’s rollout to the user’s computer is still in progress (which can take up to 72 hours).

To resolve this, make sure the software is installed or deployed using the Microsoft Admin Center. Follow this guide for detailed steps:
How to install/deploy SendGuard M365 using the Microsoft Admin Center