How to have open Layou windows appear as tabs at top of main window

I used to have all open Layout windows show up as tabs atop the main window.
Now, can’t figure out how to make that happen and somewhat embarrassed to ask.
Thanks for advice.

Do you mean open LayOut files as in projects? That happens on Windows. I believe on Mac each one will look like a separate window, the same way SketchUp does.

Duh, I found it under Window in Menu tabs – Merge Windows.
That is what I was looking for, but was not quite clear about explaining.