Unresizable Main Window Obscured by MacOS Menu Bar
On a 13" Retina MacBook Pro Early 2015 model, when launching XD, the first window that appears (presumably the primary or welcome window), where you either start a new design or open a previous one, is set to a fixed size. Unfortunately, the particular size it's set to is so large that it's covered by the MacOS menu bar on the bottom, which means it's impossible to see or read content that's underneath it unless you set the menu bar to auto-hide in the MacOS system preferences. The window doesn't allow maximization, so unless the page is large enough to be scrollable, it's actually impossible to access the content obscured by the menu bar.
For example, under the "Start a new design" section on the Home tab, the pixel resolutions of the various options, e.g., iPhone X/XS, iPad, or Web 1920, are obscured.