> Save downloading multiple updates
How can I avoid downloading the same macOS updates for each of my Macs that are running Big Sur?
Anyone with several Macs or devices can set up a Content Caching Server on a Mac, which eliminates multiple downloads. This feature used to be in Mac OS X Server, and moved into the regular version of High Sierra. To be most effective, use a Mac which is left running all or much of the time, with a good internet connection and sufficient free space, which can be on an external disk.
Although the service has advanced options, for most small networks it’s simple to set up. Having identified where these updates are going to be stored, open the Sharing pane and select the Content Caching item in the list at the left. Decide whether you want it to cache only shared content including updates, or to add iCloud content as well. Click on the Options button to set the Cache Location using the Edit button, and adjust the maximum size to what you can afford.
Settings also let you share that Mac’s internet connection, a separate decision which isn’t needed for Content Caching. When you next start up or restart your other Macs and devices, they will automatically connect to this service and your server will only download one copy of the updates and other content.