The release note says GCP Securlet was introduced as the new IaaS Securlet, but it is not showing on the Store page after the 3.156 release update.
The current store page will change. Therefore, the GCP icon will not be added to the Store page. To activate the Securlet, select GCP Securlet from the IaaS Securlet portal and click on Add Connection:
For more information, please check the GCP Securlet tech doc - About the GCP Securlet.