In an interview with news outlet MyDrivers, OnePlus CEO Pete Lau has stated that the company has shifted its research and development efforts towards camera improvements. Lau aims to bring OnePlus' cameras on par with the likes of Huawei. Hence, the company is working closely with Leica.
https://www.notebookcheck.net/OnePlus-CEO-Pete-Lau-promises-camera-improvements-across-the-board-starting-with-the-OnePlus-9-series.513903.0.html
I wish I could say I'm surprised it took them so long to finally deal with the issue, but frankly OnePlus has been slipping more and more over the years, losing what once made them great. And I don't care if they improve the cameras if they're going to continue to refuse implementing an SD slot, which is the only reason I keep skipping their devices.