I followed the instructions in https://askubuntu.com/a/1029905/340383 using this configuration:
Which seems to be correct, but the Top Bar is still showing on the right monitor (I have a left and right monitor):
Is there a switch or setting that I need to change to make this work the way I think it should?
I do have the chrome-gnome-shell installed via https://addons.mozilla.org/en-US/firefox/addon/gnome-shell-integration/
as indicated by:
$ sudo apt install chrome-gnome-shell
Reading package lists... Done
Building dependency tree
Reading state information... Done
chrome-gnome-shell is already the newest version (10.1-5).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
$ dpkg --list chrome-gnome-shell
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-==================-============-============-===================================================
ii chrome-gnome-shell 10.1-5 all GNOME Shell extensions integration for web browsers
$
Update 1
Here is a screenshot of the Settings/Devices/Displays window showing two NEC 24" monitors. The Top Bar is showing only on the right monitor (the one identified as "1", likely because I used the drag/drop inside that window to move "1" to the right, but not sure that is the root cause of this problem).
Update 2
In response to @pomsky's question, we have this output:
$ gsettings get org.gnome.shell enabled-extensions
['hide-top-panel@dimka665.gmail.com', 'alternate-tab@gnome-shell-extensions.gcampax.github.com', 'show-desktop@l300lvl.tk', 'show-desktop-button@amivaleo', 'hidetopbar@mathieu.bidon.ca']
$ ls ~/.local/share/gnome-shell/extensions/
alternate-tab@gnome-shell-extensions.gcampax.github.com hidetopbar@mathieu.bidon.ca show-desktop-button@amivaleo
$
Update 3
In response to @vanadium's comment, I opened up Gnome Tweaks, and started to do that test, but then got distracted by the icon highlighted with the red ellipse below, and then to the right of it saw that the Hide top bar extension seemed to be disabled.
Hovering the mouse over the icon in the red ellipse just shows "Error loading extension", which is pretty vague.
Update 4
Clicking on one or two of the items inside the Gnome-Tweaks/Extensions view shown above popped up a note about needing to restart Gnome. Why didn't it prompt me for that somewhere when I installed the extension? Or did it and I just didn't see it?:
Update 5
After a reboot, now the Top Bar is successfully unmapping itself until which time I move the cursor up to the top edge of the right-most monitor where it then shows itself.
Update 6
Prior to uninstalling anything as suggested by vanadiums answer, here is a FireFox page screenshot of what I see from https://extensions.gnome.org/local/
This seems to correlate with this command-line result:
$ cd /usr/share/gnome-shell/extensions/
$ ls -1
desktop-icons@csoriano
system76-power@system76.com
ubuntu-appindicators@ubuntu.com
ubuntu-dock@ubuntu.com
$ cd ~/.local/share/gnome-shell/extensions/
$ ls -1
alternate-tab@gnome-shell-extensions.gcampax.github.com
hidetopbar@mathieu.bidon.ca
show-desktop-button@amivaleo
$
I suspect the ones under ~/.local/share/gnome-shell/extensions/ came about via the GNOME Shell integration Firefox extension
Update 7
I uninstalled all of the ones I could uninstall, that had X icons to the right of them inside https://extensions.gnome.org/local/ and looked inside Ubuntu Software Center, "Installed" tab (as referenced by https://askubuntu.com/a/1171225/340383), and saw them removed at the very bottom. But then installed just one like this from the command-line:
$ sudo apt install gnome-shell-extension-autohidetopbar
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
gnome-shell-extension-autohidetopbar
0 upgraded, 1 newly installed, 0 to remove and 10 not upgraded.
Need to get 16.3 kB of archives.
After this operation, 91.1 kB of additional disk space will be used.
Get:1 http://us.archive.ubuntu.com/ubuntu eoan/universe amd64 gnome-shell-extension-autohidetopbar all 20180908-2 [16.3 kB]
Fetched 16.3 kB in 0s (64.0 kB/s)
debconf: unable to initialize frontend: Dialog
debconf: (Dialog frontend will not work on a dumb terminal, an emacs shell buffer, or without a controlling terminal.)
debconf: falling back to frontend: Readline
Selecting previously unselected package gnome-shell-extension-autohidetopbar.
(Reading database ... 404735 files and directories currently installed.)
Preparing to unpack .../gnome-shell-extension-autohidetopbar_20180908-2_all.deb ...
Progress: [ 0%] [..........................................................................................................................................................................................] Progress: [ 20%] [#####################################.....................................................................................................................................................] Unpacking gnome-shell-extension-autohidetopbar (20180908-2) ...
Progress: [ 40%] [##########################################################################................................................................................................................] Setting up gnome-shell-extension-autohidetopbar (20180908-2) ...
Progress: [ 60%] [###############################################################################################################...........................................................................] Progress: [ 80%] [####################################################################################################################################################......................................]
Verified that I had it installed:
$ dpkg --list gnome-shell-extension-\*
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-========================================-==================================-============-========================================================
ii gnome-shell-extension-appindicator 30-1 all AppIndicator/KStatusNotifierItem support for GNOME Shell
ii gnome-shell-extension-autohidetopbar 20180908-2 all GNOME shell automatic topbar hider
un gnome-shell-extension-caffeine <none> <none> (no description available)
un gnome-shell-extension-dash-to-panel <none> <none> (no description available)
un gnome-shell-extension-dashtodock <none> <none> (no description available)
ii gnome-shell-extension-desktop-icons 19.10.2-1 all desktop icon support for GNOME Shell
un gnome-shell-extension-multi-monitors <none> <none> (no description available)
un gnome-shell-extension-pixelsaver <none> <none> (no description available)
ii gnome-shell-extension-system76-power 1.2.0~1571861523~19.10~f9f05fb~dev all Gnome-shell extension for System76 Power Management
un gnome-shell-extension-taskbar <none> <none> (no description available)
un gnome-shell-extension-top-icons-plus <none> <none> (no description available)
ii gnome-shell-extension-ubuntu-dock 67ubuntu19.10.1 all Ubuntu Dock for GNOME Shell
un gnome-shell-extension-workspaces-to-dock <none> <none> (no description available)
$ date
Sun 15 Dec 2019 10:05:41 AM PST
But then the Ubuntu Software Center's "Installed" tab did not change (it did change immediately when I uninstalled the package from https://extensions.gnome.org/local/)
The behavior of automatic hiding did not change at all. It is not working at this point. So I suspected this is still the same bug whereby a reboot or GNOME shell restart is required, but they are not sending me a message stating such is required. But in this case, that stands to reason no such message is given, since I used apt install from the command-line which never has, at least for me for many years, notified me of required reboots.
I rebooted, and now the autohiding of the Top Bar is there.
What is most concerning is that the Ubuntu Software Center's "Installed" tab still does not show it, even though I've installed it via apt install, but that is a separate issue.
Best Answer
That the extension has issues may be caused by a mismatch between your version and that of the Gnome Shell version your Ubuntu Desktop is running. You are much less likely to run into issues if you install, to the maximum extent, extensions that are available in the Ubuntu repositories.
The advice, therefore, is to
Remove the extension you installed from the Gnome Shell extensions website
Install the officially packaged version using either Ubuntu Software, Synaptic package manager or with the command
sudo apt install gnome-shell-extension-autohidetopbarStill, this may not cause your top bar to disappear on multiple monitors. Your issues with having this working on multiple monitors reflects general issues with multi-monitor support by Gnome Shell that only can be adequately addressed by the Gnome Shell developers.