The System - Network Activity page of the Preferences dialog gives you full control over network connectivity. Altium Designer uses the Internet and third party servers to connect to Altium Cloud and suppliers, to search for updates, etc. It may be desired or necessary to work offline in some situations or environments. You can disable specific network activity or disable all network activity by selecting/deselecting the listed functions on this page.
The dialog is accessed by clicking Network Activity under the System folder in the main Preferences dialog (accessed by clicking the button in the top right corner of the workspace).
Click to check/uncheck each activity from which you wish to connect/disconnect: