Why do you want to hide it? Attempting to hide it will cost you floor space? Can you show the entire bedroom? Can you draw out a floor plan with ALL dimensions included?

If there are better options to decorate it instead, that would be even better. Here is the floor plan.

Since you have a nice closet you may not need a dresser, but if it were me I would put a wide dresser on the left side of the bump out. If you want to be able to watch TV in bed, put a TV over a console there. Or just a console with art over it. I can't tell whether whether that is a TV or art in the picture you posted. It is probably hung too high, but where to hang it does depend partly on what's under it. What is the curtain on the right side of the bump out covering?

Is the problem that you don't like seeing the bump out and want to hide it or is it that you are trying to fit something to the left of the bump out? Rooms have bump outs, at least yours isn't in the middle of your headboard as mind once was. I say leave well enough alone and live with it. Your bedroom is bright and airy feeling. A nice space.

It's fine as is, except for the floral curtain. I would put a nice rug down at the foot of the bed to define the space, and the bump out and niches would recede. You could mount the mirror in the narrow right niche and move your bench to the wall inside the left niche. If you put something more substantial like a dresser or TV console on the left side, I would put shelves on the right side, decorated with a very light amount of books and art objects.

My suggestion is to remove the curtain since you have a walk-in closet, place a dresser under the art and lower the art. Here's the idea...

I would install a movable vertical tower and then put baskets on the shelves and use for storage, or make it a book shelf.

We have a beam in the master bedroom,

Just a gentle reminder that posts are vertical and that beams are horizontal. Think of it as posts holding up beams.

What can we do?

I would ignore it. That may not even be a post but a framed bump out covering HVAC supply to a second floor or from the attic or sewer/ water on a second floor or venting for plumbing on a lower level. Or even exhaust from a range hood. 99.9% certain that it is there for a very good reason.

This is a nice room, the bump out really doesn't detract from that fact and even adds a bit of interest. Maybe hang that floor standing mirror on it and gain that bit of floorspace that the mirror is occupying?

One other suggestion--Hang solid color curtains that match the wall color--hang them high, just below the crown molding. Less contrast so the bump will be less noticeable.

It's highly unlikely it's not a chase of some sort. I don't understand the issue. The curtain on the right-why? That area if not needed could be utilized a few different way. I too think to the left of the chase would be the perfect place for a dresser.

You mean the bump-out? Not an issue at all. Ignore.

The curtain to the right, on the other hand, has got to go. Just put your full length mirror there (I would hang it) and it will look intentional. Get your outfit out of the closet, put it on, and check in the mirror to see how you look! 😉