This policy applies to the sign-in screen. Please see also the IsolateOrigins policy which applies to the user session.
If the policy is enabled, each of the named origins in a comma-separated list will run in its own process. This will also isolate origins named by subdomains; e.g. specifying https://example.com/ will also cause https://foo.example.com/ to be isolated as part of the https://example.com/ site.
If the policy is not configured or disabled, the platform default site isolation settings will be used for the sign-in screen.
Example value: https://example.com/,https://othersite.org/