it's kind of stark/static. Are these things real treasures? the plant real?

Something on the floor to soften the look?

What are the marbled things on each side of the hearth?

Wondering if framed art would be better than a mirror (it isn't reflecting anything great)

a plant a bit taller and fuller, in a great pot? for me, I would move things in to the mirror more.

I would spread the items out toward the sides more, rather than touching so much, otherwise it looks nice to me.

I would replace the mirror (which is similar in color to the FP and reflects nothing) with art and remove the clock for starters.

You have a good start,but the present configuration looks a bit cyclopean.
The mirror reflection is kinda blah,and items feel bunched together.
Do try an art work
about the size of the fireplace opening,hang so bottom edge is a few inches above the mantel ledge.
Instead of the clock,try another small curio item; reminders of the passage of time are not really welcome in an otherwise relaxing
space.Kudos for not putting items teetering at the very edges of the mantel.Do show us your fresh vignette!

I would paint the “chimney” section a pretty pale color.. to start

A picture from further back to show as much as possible may also inspire some more ideas…

I think the decor pieces are quite nice as is

The unique shape of the wall could be complemented with a modern layered look. To create depth and balance the recess, use a large round or abstract mirror. Make one side asymmetrical by adding tall vases, stacks of books, or sculptural items, and keep the other side clean.

A touch of natural texture (stone, wood, or ceramics) can add warmth to a modern setting. Enhance the structure of the mantel with slim wall sconces or LED strips. You can finish the look with a few seasonal greens or dried stems.

Not a fan of the pieces, as I don’t find they work well with each other. Because of the visual weight of the fireplace and the slant of the wall, suggest leaning large art and keep accessories to a minimum.

Looks like the fireplace has a faux finish and if interested, consider a venetian plaster including on tapered wall for a more unified and softer look.

There are too many hard items on your mantle. It needs items that add a big of softness.

No mirror but a nice piece of art and nothing else.