Personally, I am ecstatic that you finally gave us back that space after years of the community asking for it. Thank you! Unfortunately, I think the search bar's placement should either be moved to the menu bar (centered), or act as a small button that can be hovered/clicked to expand into the search. Possibly even give users the option to set it that way, or to have it set back to how it was before.
But as far as the individuals complaining/requesting a revert to how it was before... please, please, please do not revert back to what it was. That was a huge amount of wasted space solely for a search bar that took up <10% of the row. Again, there is still room for improvement related to this specifically, but it is clearly better than what it was before. That much wasted space in a notes app was silly. People just like to complain.
Thank you for the change. OneNote and its community deserves all the love you can give!