The Air Play icon did not show on my iMac Menu Bar and Apple TV (ATV) did not show on my iOS devices under Air Play. It did previously on all of them. Because the iMac and iOS devices all did not have the ATV access, I looked to the ATV for the problem.
An auto update on the ATV failed so I manually updated it but did not solve the problem.
On the ATV, I went to Settings, Air Play, and found it was toggled OFF. I toggled it on and the iMac and iOS devices all have Air Play to the ATV. The Air Play icon shows on the iMac Menu Bar and ATV appears on my iOS devices under Air Play.
Obviously Air Play must be on to work and it was on previously. I do not remember turning it off. My suspicion is that either the failed update turned it off, a successful update turned it off in error, or some other gremlin turned it off.
Regardless of why it was off, I'm glad I went back to the basics to ensure that everything was how it should be even though it worked before and I did nothing to change it. (or did I?)