The photos you like best show very little on the mantel; so copy that in your scale. Consider a bigger mirror to cover most of the area. I was going to suggest sheet rocking the upper area, but notice the ceiling may have openings of different size.

It's pretty crowded there. I'd take everything out, mirrors included, and put back the vase. And that's about it. Try that, see how you feel about it, maybe add one more thing but put all the small bits and pices somewhere else.

Your three inspiration photos are very different styles but all more streamlined than what you have. What style works with the rest of the room? Unless you have a very formal room the middle inspiration photo seems best suited to the fireplace and would be easiest to recreate ( and inexpensively. )

Gentle reminder to take off the command hooks.

Have you considered painting the gold accent strips with heatproof black matte spray paint ?

Your inspiration photos show that you have excellent taste . So, all of those should tell you that nothing you have up on top of your fireplace fits or looks good . Take it all out and get a bold round glass vase and display a few large flowers filling the space ...or a sculpture ..or an ornate , wicked candelabra ... You seem to love the creative ....find something special for that space ...and or put a spotlight in the middle , shining a light on something you love ...! Be as creative as you have been looking for your favorite photos ...find something new to put there and enjoy ! It takes time for a special look . Take your time ...after you take everything off ! ..

Using the things you have, I would leave the mirror where it is, the three things (wooden?) where they are and then on the other side the small vase with the grassy plant in it. The rest can go elsewhere.

I would look for art you like instead of a mirror. The art should be about the size of the firebox opening, or maybe 3/4 of it. Mantels are always best when kept simple.

You said it....”a jumble of unrelated and mismatched garbage”. Too too too much stuff! A corner mantel is impossible to begin with.
Have you considered having the corner hidden by a new “wall” straight across the corner, set back a couple of inches from the edge of the mantel? Then you can hang a piece of art and be done with it.

Good advice here about how to get your space more aligned with your inspiration photos. I would just add one thing to consider as you rework the mantle. Notice that all your inspirations are quite monochromatic, whereas your current decor has five or six different colors. So as you rework the space, keep the colors limited if you want to create something like the inspirations.

thanks everyone, great advice and I completely agree with each person's comments. unfortunately I cannot accomplish a few as I rent and cannot leave any permanent changes behind for the owners. I think the art instead of mirror , and taking the time to find something new .. something not somethings like so many suggested will be the way to go!

Some ideas

Geodes seem to be your thing. Take everything out of there and very simply display those. You’ll need some elevation, but candlesticks aren’t it. Blocks of wood or acrylic or something similar.