This is something between a bug report and a product suggestion. Unfortunately, Endnote does not support Dark Mode which results in strange behavior when you try to insert a citation in Word for Mac 2016.
Here’s the original support request I sent the support team:
Since upgrading to macOS Mojave and enabling Dark Mode, the “Insert Citation” window in Word for Mac 2016 has two problems:
The text color in the lower pane (bibliographical information of the selected literature) is set to black instead of white which makes it almost impossible to actually read the information.
When literature is found, the list is, at first, not displayed in the top pane of the window. However, you can still go through the literature using the mouse/touchpad or keyboard and you can see the bibliographical information in the lower pane change accordingly (black on dark grey, as stated above). If you then close (using the “Cancel” button) and reopen the window, the search results are shown in the top pane (white on dark grey, as it should be). Also, if the search results exceed the size of the pane, making the pane scrollable, and if you actually scroll through the search results, the visualization kicks in and the results are displayed correctly (i.e. without having to reopen the search window).
I would have posted the URL to the screen recording I sent the support team, but that’s not allowed. You will have to make do with a screenshot.