I am not using UEX. I use UltraEdit for Windows. So I cannot really help with suggestions which I could try myself before posting them here.

My first suggestion is increasing the screen resolution. But this is most likely not possible due to hardware display of old notebook supporting only the display resolution 1024x576. The height of this display is below the minimum defined (by Microsoft in 2001 for Windows XP and all later Windows versions). For Windows XP was defined a minimum display resolution of 800x600. I read about that 20 years ago in the Microsoft guidelines for programmers developing Windows GUI applications. It is also written in Wikipedia article about display resolution. I am quite sure that the Gnome Desktop developers and the Debian 10 developers and UEX developers expect also a minimum display resolution of 800x600 as it was and is the de facto standard for GUI applications. Debian 10 can be definitely used also with computers having a display with a resolution below this minimum, but then mainly in text mode (terminal only) and not with GUI applications which most have larger, non-resizable and non-scrollable dialog windows. A dialog window is technically completely different to a document, view or list window which are by design resizable and scrollable on all platforms due to completely different requirements on contents display in comparison to a dialog window.

My second suggestion is using the keys to navigate to the buttons and activate them. The key TAB can be used to set focus from one item in a dialog window to next item in dialog window. So when no visible item has anymore the input focus after pressing multiple times key TAB, the first button OK has most likely the input focus and pressing key RETURN or ENTER activates it to take over the modified settings from any preferences window and close the preferences dialog.

There is always defined for a dialog window the default button which is (most likely) the button OK for the Preferences dialog in UEX. So pressing key RETURN or ENTER with input focus set on a dialog item not being a button results in activation of default button with applying the changes made in any preferences dialog window and closing the preferences dialog.

Note: Many users think, they must first click on button Apply to apply the changed settings and next click on button OK. But this is not true. Apply takes over (applies) the changed settings and keeps the dialog window opened while OK takes over (applies) the changed settings and closes the dialog window like the button Apply and Close which I have seen in the meantime in some applications instead of OK due to missing user knowledge about function of button OK. Further, the buttons OK and Apply are for all settings and not just for the settings in current displayed dialog window in a Preferences dialog with multiple preferences windows selected via tabs, a list or a tree  inside the dialog window .

There is perhaps the possibility in UEX to decrease the size of the icons. It looks like 24x24 is the currently used icon size. It would be better to change the icon size to 16x16 if that is possible somehow on a display with a height of just 576 pixels.

My last suggestion is to connect temporarily to the notebook a display with a higher resolution to configure UEX. You have perhaps a digital TV which has support for a VGA connection as your old notebook and so you can use your TV temporarily to configure UEX.