Do you mean 9pt or 9px font? Either way, that's not comfortably readable on a 32" 4k screen.

On a 34" 3440x1440 screen I keep IntelliJ at 14px (10.5pt). On a 32" 4k screen I keep it at 15px-16px (~11pt).

You're still only talking ~100 lines of code on the screen at any one time. Maybe ~130 with a smaller font.