I am just wondering since it doesn't have any requirements pertaining on using breathing style techniques you just only need to learn how to use it with proper training, Does it mean it is possible for a demon to use it?
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 the Breath of Wind. And now as a Demon with an adept Demon Slayer Breath style(Breath of the Moon).