Can I say shema if I’m not tznius
It is preferable to be tznius and that one’s chest be covered when saying kriyas shema, but technically you can say kriyas shema even if you aren’t tznius. A man however has to be careful to make sure that there is a separation between his heart and erva “l’bo roeh es ha’erva”. Therefore he should either be wearing underwear that is up against the body, a belt or by placing something, even his forearm, against hi body that will separate between his heart and erva (genitals). He must also be wearing something to cover his head when saying kriyas shema.
The halacha of “l’bo roeh es herva” essentially doesn’t apply to women according to most poskim. For a woman to be careful about this would be a pious act.
Shulchan Aruch O:CH 74-1, M:B ibid 1, 16.