I should say "measurable in task manager" - which reports in increments of 0.1%.

Realistically I would imagine that a native Win32 app (Notepad++) that's totally idle except for message loop and cursor blink requires less than a microsecond of CPU time per wall clock second.

It gets better: the caret in "real" Win32 is not rendered to the framebuffer or any memory-backed surfaces, but is "inlined" in the video output the same way the (hardware) cursor is - it's effectively an old-school console sprite.

But it does mean you're limited in the things you can do with it - when Office 2013 gained that fancy animated caret they had to do it themselves, similarly the caret in Atom and VSCode are both software-based.