Thank you for posting here in the Community. I can share some insights about changing the appearance/resolution/font on the printing screen in QBO.
Currently, your request is unavailable. As mentioned by Rustler, you can adjust your monitor setup or brightness in order not to strain your eyes.
I also think it's a good idea to have the option about the appearance, resolution, and font. Rest assured, I'll be sending feedback to our Product Development Team based on this interaction. After all, enhancements to QuickBooks functionalities are largely the results of feedback provided by users, such as yourself.
You can also do the same by clicking the Gear icon and choosing Feedback.
Let me know if there's anything else I can do for you. Just add a comment below. Have a good one.