"Show monitors in panel" does not work
This issue is found on Trisquel 11 Aramo MATE with the default MATE panel.
How to reproduce the bug?
System > Preferences > Hardware > Displays, select "Show monitors in panel". No monitors icon is shown on the default panel.
How do I know it is not a bug in MATE but in Trisquel?
System > Preferences > Look and Feel > MATE Tweak > Panel, change the panel layout from "Trisquel" to "Traditional", then "Show monitors in panel" works. I also checked the MATE in Linux Mint which also has a customized panel, but it does not have this issue.