Q: Why won't iTunes 12.5 open in full screen on my pc?

I know I can do all of that. But it used to just "happen" automatically when I launched the program.

Just figured it out. There was a persistent little nag from Apple introducing Apple Music or something when I launched the new iTunes. It stayed on for about a half-second before opening iTunes in partial screen view. I quickly clicked the "no" option button before it disappeared and iTunes now launches as it always had before...in full screen WITH the sidebar. Yeah!