An ArcGIS Enterprise deployment is completely internal and does not have access to the internet.

For environments without internet access, the organization can use the patchnotification.bat utility to check for available patches and updates. This utility can be run from the command line and provides information about the current patch status of the ArcGIS Enterprise components. Administrators can then manually download the necessary patches from another machine with internet access and transfer them to the internal environment for installation.​

Reference Source: ArcGIS Enterprise documentation on checking for and installing software patches and updates​