How do I remove the ability to move the cursor after then end of line in IntelliJ?
By default, it's turned off (unchecked).
If it is turned on, you can use one of the following 2 approaches:
File > Settings... (or Ctrl+Alt+S) > Editor > General > Virtual Space section > uncheck Allow placement of caret after end of line
Help > Find Action... (or Ctrl+Shift+A) > type "Virtual Space: Allow end" > Enter or left click (to switch between On and Off) > Esc