Is it possible for a Demon to use a breathing style technique?
Yes but I might be wrong in some details;


   Kokushibo is a member of the Twelve Demon Moons, holding the position of Upper Moon One. In his Human life, he was a demon slayer who trained him by a Breath of Wind user. And now as a Demon with an adept Demon Slayer Breath style(Breath of the Moon).