Enable a window without titlebar in all workspaces

I have a window (Google Hangouts App, to be precise) that I want to show up on all my workspaces. However, the window dosen't have a titlebar, so I can't right-click it and untick Only on this workspace.

Any idea?

Solution 1:

The alt + right click was a good advice, but didn't worked for me, after trying a lot I've realized the windows key + right click brings up the title bar menu in my case (Ubuntu 18.04, Gnome 3.28)

Solution 2:

You can access the titlebar menu via alt+right-click.

I've used this trick for the exact same thing you're looking to do, and it keeps hangouts on all workspaces for about a day. The next day I have to do it all over again.

I'm testing the answer in question 37129 with the window name (you can't use the window class), but I don't know if it will work consistently or not yet.