Can I open the bedroom door under the stairs?

No, it is possible to feel more ventilated and cool, but there are several disadvantages:

As far as life is concerned, it is unsightly and sometimes inconvenient to see the bedroom as soon as the door of the stairwell is opened.

From the perspective of geomantic omen, this will easily lead to the invasion of evil spirits, which is not good for the people in this bedroom.

If the house has been built, remedial measures: put a shoe cabinet in the proper position of the stairwell door to block the evil sight outside, or set a screen about one meter at the door of the bedroom, or hang a big picture, which not only increases the aesthetic feeling, but also has the function of partition. It is recommended to use the previous method.