My Mac is downloading a new update and it is hogging the internet so I can't work at all. How do I throttle the speed?
Here's an example of how it's done in Windows:
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The store downloads for apps and updates use the system speed. You can throttle that as a whole, but not for any store downloads.
Short term, pause the download if your router can’t assist you. Longer term you might be happy with one Mac on the network subnet caching downloaded content so you only download it once.
Content caching (available in the sharing preference pane) has all the knobs, settings and tweaks you might need to manage things better than on and off.