Due to a bug/glitch, I can't use Gnome Flashback for a while. I am forced to use the new Gnome 3 layout.
There are a few apps (Slack, Skype, Steam, KTorrent, Krusader, ...) that used to be minimized to a "tray icon" in the "task bar" or "notification area" or "indicator applet" or whatever, I am not quite sure about what the names are. It's the little icon somewhere in some bar which you can click to restore the app or show a menu.
In Gnome 3.26 (and later versions), there is no such area by default, and the apps, once minimized, disappear from GUI entirely. I can't see them anywhere, yet their process is running.
I am not going to criticize that decision (it's obviously a bad one :) ) and will skip to the questions:
How am I supposed to open such app?
How can I configure Gnome 3 to have that running apps icons area?
I have seen these (K)StatusNotifierItem/AppInicator Support and TopIcon Plus. Are these official? Or will it stop working in the next release as these workarounds tend to?
Install (GNOME) Tweaks by running
Open Tweaks, under "extensions", there is "Ubuntu appindicators". Enable it and you should get that icons area.
If "Ubuntu appindicators" is not installed, install it first by running