The Securly SSL certificate is essential to filter HTTPS sites correctly. You can push the Securly SSL certificate using a Microsoft Endpoint InTune by following the steps below:

Sign in to the Microsoft Endpoint Manager admin center
Select Devices > Windows > Configuration > Create then select new policy
Select ‘Platform’, ‘Windows 10 and later’, and then select ‘Templates. Search for Trusted certificate and then click on the Create button.
Name the profile.
Upload the Securly certificate (Base-64 encoded X.509 CER) to the 'Computer certificate store - ROOT'. Securly Certificate
Assign the Securly certificate to the Security Groups and then select ‘Create’ in the final step.

How to push Securly SSL certificate with Microsoft Endpoint InTune