Let me guide you on how to reduce the size of your QuickBooks Online screen.
Use these shortcut keys on your keyboard to reduce the scale of the page:
Press the Ctrl and + (plus) keys together to zoom in.
Press the Ctrl and - (minus) keys together to decrease the scale
Press the Ctrl and 0 (zero) keys together to reset the scale to 100%.
In addition, you can also click on the ellipsis icon (⋮) from your Chrome browser and click on the minus (-) icon to reduce the screen size. Or press the Ctrl and minus (-) icon on your keyboard.