In order to minimize flicker, I start with the main window invisible, then make it visible in a time.
That did not work : I got a painful flicker, as a Container Control was embedWithin.
It appears that no matter the Container Control initial visible state, doing embedwithin shows it, and in the process, shows the window.
Not fun. Not fun at all 
I just verified this in OS X as well with 16r4.1 … Any EmbedWithin or a ContainControl to the Window results in the window showing regardless of its visible state. At least on OS X it doesn’t flicker.
Have you filed a report?
Not yet. I wanted to verify I was not in error.
Will try to do this today.
Have you seen a difference between 2016R3 and 2016R4.1 ?
I do use embedwithin in my project witch is Windows + Mac. No problem at all on Mac, but flickering got even worse in 2016R4.1. In fact, not acceptable anymore, so had to stay with R3.
I reverted back to 2016R3 for several other reasons as well.
OK. This morning I tried to create a sample project to demonstrate the issue, and it does not behave as I saw in my bigger project. There must be something I forgot. The plot thickens …
Does your larger project’s ContainerControl set properties or call parent window methods in its Constructor or Open event? It appears that since mine did, that may be the cause of what I saw on OS X. I still don’t think it should happen if the parent window’s Visible state is set to False, though.