GIMP Version: 2.10.14
Operating System: Linux
OS Version: Ubuntu 18.04
GIMP Experience: New User

List any relevant plug-ins or scripts:
No

List any ERROR messages you received:
Hidden buttons

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While trying to change the icon set through " preferences ", "save " button and other buttons are hidden. I tried resizing the window without any luck. How to keep everything under visible space ? Thanks.

Ubuntu 18.04

First, click the down arrow after "guess icon size from resolution" and set it to custom size. Use the slider to set icon size to small.
Moving big dialogs in Linux: Alt-click the dialog and drag over the screen edge to reveal hidden buttons.
Click OK. That saves the icon theme and size you have chosen.



You could use other tweaks to get more space like disabling any tools you don't use that often: Preferences, Interface, Toolbox.
Desktop appearance settings, default font also affects the Gimp GUI when you're using built-in themes.

I'd browse gnome-look.org for a custom theme, optimized for small screens if I had 1368x768.

Thanks. I tried. In the end, there is a very small portion outside the visible range. That part is almost of the same size as the top bar in 18.04 Ubuntu.