Microsoft message WI-FI not secure.

> Model: RAX40|Nighthawk AX4 4-Stream WiFi Router

   RAX40[v1] or RAX40v2?  Look for "Model" on the product label.
Firmware version?

> I believe that I have an updated router [...]

   Who cares what you believe?  What can you prove?  What, exactly, does
"an updated router" mean to you?

> [...] Wi-Fi network that's not secure because it uses an older
> security standard [...]

   Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation.  Get the User Manual (at least).  Read.
Look for "Specify Basic WiFi Settings" and "Change the WiFi password or
the WiFi security".  Choose a security option with only WPA2 and/or WPA3
in it.

      Your router comes with preset WPA2 or WPA security.

   Apparently, expectations have risen since that decision was made.

> [...] need to know if the Microsoft notice affects my computer system.

   It means what it says; your router's Wi-Fi security is not up to
current expectations.  So change it.