Thanks that works partly.
Two points.
1. In the video, File>Open from an existing workbook opens the new excel and adds to group. This works the same way for me now.
However, in the video, using the + sign opens a new tab in the File>Open view. For me it opens with a blank workbook. So, to open the desired workbook by using +, there is now another step required, of going to the new blank workbook and then File>Open
2. The "psychedelic resizing" has a pattern. If the Group window is in window (non maximised) mode when a new tab is opened, there is no problem and the opening is smooth.
But if it is maximised when a new window is opened, each window first opens in the window mode and then resizes to maximum. That causes the sequence of resizings that I was referring to.
Are these bugs or am I missing something?