Given news wrote:

Basically, Windows chooses the fastest link. You can override this by
adjusting the automatically assigned metric. To adjust the metric, open
the adapter properties Internet Protocol Version 4 General
Advanced and disable Automatic metric. The adapter with the lowest value
is the one Windows will choose.

Thanks to that info, I found that "automatic metric" checkbox.

Here is a picture of it on my computer desktop.
https://www.turboimagehost.com/p/35488920/wifi.jpg.html

If you only need a particular adapter to be used temporarily, it might
be easier to either manually disconnect from wireless or disable the
adapter (right-click Disable), rather than setting the metric manually.

At this point that's exactly what I do which is I either pull the Ethernet
cable out of the one wifi antenna connection at the back of the desktop or
I pull the usb stick out of the usb port at the back of the desktop.

Right clicking and disabling would also work as you noted.

What I will try to figure out is how to *set* that metric so that I can
just set the adapter metric to, say, 25 for the adapter I want to win and
50 for the adapter I want to lose, and when I want to switch which wifi
connection it uses, I just reverse the "cost" metric.

That web page you referred me to seems great but it's complex the first two
times I read it.

An explanation of the Automatic Metric feature for IPv4 routes
https://support.microsoft.com/en-us/...or-ipv4-routes