A list of domains that Automation Suite and the bundled products need to access to function as expected. You must allow traffic to and from these domain, otherwise Automation Suite may malfunction
What this is saying is that in the server where you plan to perform the installation, the server must be able to reach https://download.uipath.com as during the installation it will download the installation files automatically.
This is only applicable if you’re performing and online installation (i.e. the server has access to the internet). If you’re performing an airgapped installation (i.e. the server does not have access to the internet), then you’ll need to download the installation files on your own and upload them to the server. There is no need to have access to https://download.uipath.com if you’re performing an airgapped installation. The installation files can be found here: Automation Suite - Downloading the installation packages (uipath.com)