Unfortunately that might be the only option it seems to get the old behavior back, which of course is not an option for those working in corporate environments with update policies and such. Things like this were actually one reason our company was previously on the semi-annual update channel of Office 365, so that we wouldn't get random breaking changes like this pushed out with no warning.
And it worked well - for example, the semi-annual channel build of OneNote had the old search functionality long after the other channels (monthly enterprise and current) had the new broken search. But of course, MS then implemented Copilot and made it available only on the monthly enterprise or current channels. And since nobody can live without AI these days, the push for that forced us to go to the monthly enterprise channel. And then changes like this come down the pipeline, demonstrating the exact reason we didn't want to be on such channel.
Ugh, at this point I don't even know what to do. For my own personal subscription, I could consider the perpetual route although you know it's only a matter of time before so many new features get cut out of the perpetual products, users will have no choice but to move to subscription-based. And then with subscription-based they force these changes down your throat and don't listen to feedback even when everyone is screaming the same thing. In the corporate environment where everyone wants the latest AI features....it seems we're pretty much SOL. Again, just an overall terrible user experience.
I used to be the person recommending OneNote to anyone who was interested, anytime the topic of note-taking apps came up. The worse this search experience gets, the less it makes me want to support/recommend it.