My ceiling height is 8 ft. What material should I use for the fireplace around to achieve this? Matt black look

Are you keeping that fireplace insert?

That inspiration photo works because the TV is much narrower than the rectangular fireplace insert. A rectangular TV over a much smaller "square" fireplace insert is going to look unbalanced or top-heavy.

I am open to the option of replacing the fireplace with a linear one. The black portion of the fireplace is 45 inches wide. My television is 48 inches. It all could work, but I am also a bit concerned about heat from the fireplace affecting the electronics in the TV.If I use a wider mantle, say 10 inches or possibly bigger that could help.

i'm also looking into fireplace options so i have done a ton of research. it needs to be non combustible so the options to get the matte look are 1) large format matt black tile (but there will be some micro grout lines they can tint the grout black) this is probably a more affordable option. 2) quartz or porcelain (like a backsplash or counter they can cut to measure and you can get a honed or matt finish), 3) black sheet metal again this is custom panels cut to measure.

Your fireplace looks great as it is. If you lower the mantle, it's going to be out of proportion to the fireplace permanently. I think putting a TV over the fireplace isn't worth the mess and expense you're going to get into.

With the right amount of money you can do anything. You’ve gotten good advise on proportion.

While I too like your fireplace as is, I understand wanting to modernize.

However, my least favorite option for a TV is over a fireplace. I would only do that as a last resort.

You obviously already have a TV someplace else, why is that not working?