Sounds like you're having problems similar to some that I've been having in the past couple of months as well, good to know it's not just me. I wasn't sure if it was something with my setup or not, but even after disabling all add-ins, rebuilding Windows search index and clearing ON cache, I'm still having issues with search since they made this change (unrelated to the UI/workflow issues it causes which of course is the main thing everyone has been discussing) - these are functionality issues. I've reproduced this myself on at least two different workstations.
One is that when I change scope for search, it loses focus so I have to click in it again to type my search. This is a problem for me since I am used to setting the search scope and then start typing to search - that's how it's always worked before, and that's how it still does work the 2nd time I do it for some reason - but the first time I click the dropdown arrow and set the scope, it always loses focus. That means whatever I started typing for my search the first time ends up getting put at whatever random place on the page my cursor happens to be at, which messes up my notes obviously (especially code snippets I have in them that now have syntax errors because of random characters inserted because of this issue). Also I have noticed as well the Ctrl+E and Ctrl+F shortcuts don't work nearly as well as they used to - especially Ctrl+E never seems to work anymore.
Tony He , in addition to the UI issues it seems there are some bugs introduced with the latest changes. For someone like myself who uses search probably 50x a day or more, this is becoming a major problem. Please, can we try to get these bugs worked out and add the option to move search back to where it was. This is not that big of an ask (basically just asking to go back to what we had 3 months ago that everyone was happy with and nobody wanted changed)...but it would help users immensely. The majority of us are not just using free OneNote, we are paying Office customers. Please, listen to what everyone here is saying...we are all busy with our jobs and lives, yet this is obviously important enough to this many people to take time out of their days to come on here and post about OneNote (which I guarantee you was not originally on their to-do list). That should show you how important this is to your customers.