How do I tell Windows to STFU when I play games?

Hi, you have stated the problem, but not the sort of solution you seek. I'll assume you want control of Windows update downloads.

This method is widely publicised and is one way to stop updates.

You would have to reverse it to allow updates, noting Defender updates are reliant on Windows updates.
However, you can set up a scheduled task to update Defender independently of Windows Update.

Set your connection to metered to stop updates being downloaded
This stops updates being downloaded and works for both ethernet
http://www.windowscentral.com/how-se...red-windows-10
and Wifi
How to set metered connections and disable Windows 10 Update Delivery Optimization | Windows Central

If you were to use a script to enable the setting, and another to disable it, that would be convenient.

Also see:
Windows Update Automatic Updates - Enable or Disable in Windows 10 - Windows 10 Forums
from the Tutorial section, which it's well worth being familiar with.

(IDKW STFU means. - I don't know what that means).

I would consider them violated-- thanks!

STFU = Stop The Freakin' (auto)Updates..

By way of digression...
Personal choice is tha I block WU in firewall... but thougt I'd try WU again wth this CU.... Wow what a long-winded palava of configuring and stuff...on the positive side my drivers for the old laptop installed fine - used to fail before.

Apart from Office, quite happy downloaing the CU (cab or msu) instead - works much better.