Missing window list on bottom panel in gnome-classic

Solution 1:

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You will need to use one of the shown panel-applets.

Press Win+Alt and right-click the bottom panel bar - N.B. Win is the Windows Symbol key

(If you are using Gnome Classic (No Effects) i.e. gnome fallback mode then to add to the panel use Alt and right-click)

Lots more information and some very useful links to customise your classic desktop can be found in the linked question.