At this time, QuickBooks Online isn't able to change the font of the reports. The font that's showing up is the default set up in the system.
However, if you wish to change the font size for better viewing of your QuickBooks Online, you can hold the "Ctrl" key and press the "+" sign simultaneously on your keyboard. Or, you can hold the "Ctrl" key and then scroll up.
You also have the option to change the font of the report by exporting it to Excel and modify if from there.
To export the report to Excel:
Click on the export icon beside the small gear icon.
Tap on the Export to Excel option.
I understand how seamless it would be to have an option to adjust the fonts directly from the Reports'page. Rest assured our developers are continuing to improve QuickBooks to deliver the best experience and cope with your business needs.
To stay updated with our latest news and product road-maps, you can always visit our QuickBooks Online Blog site regularly.
I'll be around if I can be of further assistance with QuickBooks. Just let me know by leaving a reply below. Have a great weekend!