How do I increase the overall font size for the AI application?

The size of text elements in the user interface is influenced by settings both within Adobe Illustrator and settings in the operating system. UI scaling settings within Adobe Illustrator are found in the Preferences menu (under User Interface). If you're using a Windows-based PC right click on the desktop and choose "Display Settings" in the flyout menu. Under the Scale and Layout setting there is a drop down menu with a bunch of percentage levels for scaling text and other UI elements. It's likely you'll need to experiment with settings from both of those dialog boxes to find the right balance.