(my-partition-randomly '(a b c d e f g h i j k l) 4)

'((a b c) (d) (e f g h) (i j k) (l))

(defun my-partition-randomly (list max-length) ""
       (let ((result '()))
         (while list
           (push (seq-take-while (lambda (x) x)
                                 (map 'list
                                      (lambda (x) (pop list))
                                      (number-sequence 1 (+ 1 (random max-length)))))
                 result))
         (reverse result)))