I prefer the search bar to be discrete when not in use, but it was too narrow previously for easy use.
The ideal solution for me would be that the search bar is like Option 1 or the original 20.0.30 in your images when it is not in use, leaving the maximum width for information in the centre box. The 20.0.30 version is good in that it is only wide enough to display the word "Search", so a user can see what the field is for. Then when in use the search bar should expand left, either to about a third of the width of MC, or to fit the text typed into the box.
Expanding it to a third the width would be easier programmatically, but probably less attractive.
Expanding to the width of text entered would take a bit more programming, would mean the text moves left as you type, and could result in redraw issues, but would be the best solution from a functionality and visibility point of view. Perhaps expanding the bar by ten characters at a time as required would work better than doing it as each character is typed.
I have used a program, many years ago, that had an expanding search box, but it was left aligned and there was space to the right to expand into without adjusting other elements on the screen. Still, it was a nice feature that resulted in less clutter on the screen when the search function wasn't being used.