Slightly OT? WiFi problems

[MR ZenWiz]

I have a Linksys AC2200 router located in my office at home.  My
desktop is wired into it, along with 2-3 others (can't remember, can't
look).  They seem fine.

My partner's main lap/desktop is across the room and connects to the
WiFi easily.  My personal laptop is two rooms away behind me, and it
connects just fine.

We have two other laptops more remotely located behind a few walls
that are concerned here.

The closer one is in our bedroom (mainly for entertainment via the
web). It is an old (probably > 10 years) Windows 7 laptop on which we
run Xubuntu 20.04.  This machine was working with the wifi just fine
until two nights ago when it dropped the connection and has not picked
it back up since, despite my best efforts to awaken it.  I'm pretty
sure the wifi device in the machine is working fine because it can see
our neighbors' wifis, outside the house.

The farther one is a relatively new Dell Inspiron, in our bedroom
closet (long story) that connects just fine to the wifi.

How can I determine what is going on with the wifi on the
Win7-cum-Xubuntu laptop?

We've moved the router's "antennas" around, raised it to a higher
level, moved the laptop around, but no success.  As I said, none of
this was happening until two nights past, and now it stubbornly sits
alone on the HDMI-TV cart, underneath, where it has been since we had
to set up this arrangement.

I've tried telling it to find a hidden network and given it all the
right information - no connection.  I've tried setting up a new
connection - won't connect.

The only thing I haven't tried so far is to unwire the laptop and take
it into the office near the router to ensure it can see it up close
and personal. I will do that when I can.

I've Googled for this, but 90%+ of what comes back is Windows related.

Where can I look for more data that might help? Any other suggestions?

Baffled.

Mark