F28 XFCE Display dialog not allowing mirroring

[Robert Moskowitz]

I did an update yesterday, and now I cannot mirror my external monitor 
with my laptop screen.

Best I can do is for one to be displaying content and the other allowing 
windows moved to it.

I have had this problem in the past, and fiddling with screen size or 
rebooting has gotten mirroring turned back on, but not this time.  Any 
hints?

I am starting to build my F30 system, but I do want this one to work 
properly.  At least for a bit more time.

thanks