Thanks for reaching out to the Community for support. I understand how frustrating it can be when the QuickBooks Online app has super small text. Rest assured, you came to the right place to get this sorted out.
Since the error message states, "Your browser seems to be zoomed. Please reset it for the best experience", let's reset the app data. Resetting the app data plays the same role as clearing the cache from your browser. Both the app and browser stores cache to save time when loading repetitive data and images. These files can often become outdated and corrupted, causing issues like the one with your text being small. I've included the steps below to reset the app data.