I downloaded Arduino 1.8.12, in the OSX 10.15.2 (Catalina) environment, with dual displays hooked to a MAC Mini. If I move an IDE window, or the Serial Port window to the alternate display, life is fine, until I try to move it on the alternate display. Then poof!, all is gone, except a dialog box stating that Arduino quit unexpectedly. You bet it did.
Has anybody had this problem, and how do I officially report something like this to the Arduino staff?