After this prints "all bad", try M-v (scroll-down).

emacs-27.2 -Q --eval \
  "(progn \
     (switch-to-buffer \"xdisp-tests--scroll-down-leaves-cursor-behind\") \
     (insert \"Óscar\" \"\n\") \
     (dotimes (_ (/ (1+ (window-pixel-height)) (line-pixel-height))) \
        (insert \"line\" \"\n\")) \
     (goto-char (point-max)) \
     (redisplay) \
     (scroll-down) \
     (redisplay) \
     (princ (format \"all %s\n\" (if (= (window-start) 1) \"good\" \"bad\")) \
            (function external-debugging-output)))"