Sorry that Photoshop opens all documents in grayscale after the recent update.
Would you mind try resetting the Photoshop preferences so that if there are any corrupt app preferences they will get restored to default? https://helpx.adobe.com/au/photoshop/using/preferences.html Press and hold Alt+Control+Shift (Windows) or Option+Command+Shift (Mac OS) as you start Photoshop. You are prompted to delete the current settings. The new preferences files are created the next time you start Photoshop.