Anyone who serves as a Lector, Communion minister, usher/greeter etc should be dressed modestly & in at least, type business casual clothes at minimum in my opinion.
Ideally, the same for the congregation too for anyone over the age of reason ( age 7 ).
I do remember feeling resentful when my sister (at the time age 15) came to the Mass held for the graduates (that I was in as I was graduating high school - the church honored both high school and uni/college grads in the church each year in June) wearing a tee and long shorts, and Air Jordan tennis shoes. Why my parents didn’t make her wear a regular shirt and pants (or even culottes, perhaps a skirt), I will never know.
Another time, years later, she came to our grandmother’s funeral Mass wearing a light colored business style suit with pants. The jacket and shirt were skin tight, and exposing some cleavage. I understand my sister is a lapsed Catholic but I thought she knew better.
I know my mother complains about my cleavage, but I know to cover it up when going to church with a business style blazer, a sweater, or a shawl. I remember being all dressed for a concert out of town, and went to a church, and covered my cleavage with a sweater that was easily removed in my car after Mass as the long dress with cleavage exposure was fine for the concert, not for church.