If you connect via dial-up or USB connection to a DSL/cable modem, and have
no home network, the Client for Microsoft Networks is of little value or
interest for you.
If you do have a home network, or connect to the internet via an Ethernet
cable, it may be necessary to have this, but not for Windows Defender. But
to install the client, go to your Control Panel, switch to Classic view if
necessary, go to Network Connections. On your Local Area Connection icon,
right-click, hit Properties. Hit Add, then Client, you should be able to add
Client for Microsoft Networks from there.
To solve the Windows Defender error, just download & install the latest
Defender over top of your older version from the Microsoft website - DO NOT
uninstall it first, or uninstall and re-install from your old backup of the
"Windows Defender.msi" installer file. The Beta versions have licenses that
have expired based on the date/time in the clock on your system tray
(bottom-right corner), which by now, if your date/time is accurate, is past
the date the Betas were meant to survive until, if the rash of these errors