There are lots of questions about how undergrads should address professors, but this is about the opposite. Context is North American research university.
My instinct and personal preference is to ask undergraduates to address me as Professor Lastname or Dr. Lastname until I let them know otherwise. And I have no problem with explicitly saying this in my syllabus for a class.
But then sometimes I think "actually why aren't I addressing students as Mr./Ms./Mx/(or some honorofic) Lastname".
Should I do so? Do you do so?