In general, it can be set. If you can't set it, you can try to update and upgrade your mobile phone system and reset it. Xiaomi note font size setting method is as follows:

Click "Notes" to open the mobile phone desktop;

Click the menu button in the lower left corner of the mobile phone screen, and click "Settings" in the pop-up window under the note interface;

Click "Text Size" on the opened "Settings" interface;

Then select options such as small, large or oversized in the "Text Size" window that pops up at the bottom of the interface.