I'm on Emacs 28.0.50.  I believe cl-print-object method code is not used when it
should be.

emacs -Q

C-x b *scratch* RET

(require 'eieio) C-x C-e RET

(defclass test nil nil) C-x C-e RET

(defmethod cl-print-object ((x test) s) (princ "#<test>" s)) C-x C-e RET

(make-feature 'test) RET C-u C-x C-e

For me, this prints like a structure (?): #s(test)

Now,

C-x 3

M-x ielm RET

(make-feature 'test) RET

This does make use of cl-print-object method:

#<test>

Structure method seems to also be used in org-babel evaluations.