Echoing everybody else's sentiments here - please at least give us an option to move this back to the old location. For people like me who use horizontal tabs, there is absolutely no gain from this change - the horizontal strip that used to contain the search bar in its old location is still there, because it also contains the horizontal tabs. So I regained 0 screen space, but my workflow was significantly disrupted regardless as the search box now overlaps many long titles, as well as page content when expanded. I won't even try to imagine how mad someone who writes in right-to-left languages would be; this change would likely make the product almost unusable for them.
I appreciate that you guys are looking for ways to improve OneNote, and collecting (and hopefully listening) to customer feedback - that's great! It's an amazing product. And I never miss an opportunity to let people know this when the topic comes up. But the bottom line is, to put it as politely as I can - this change was not well thought out. So please, keep OneNote a great product by being responsive to customer feedback, by testing changes much more thoroughly before pushing them out to production/mainstream update rings, and ideally by making future potential significant UI changes an "opt-in" experience rather than a mandatory experience that doesn't even have an "opt-out".