The hole is from an AC unit that previous owners put in. Wondering if I should fill it in with brick. Eventually I want built ins but need to make it look better for the meantime. Here’s one more photo.

If it's 'for the meantime' there are lots of diy options for fake bricks online. Even seen them done with styrofoam! Stick them on a board that coverthe hole, paint white and you are done!!

Tall piece of furniture, or faux brick.

A tapestry could work and then move the two items underneath and add a large clay pot with twigs. End up with not only covering the hole, but creating much more interest to your fireplace

Post a photo of the whole wall from far back. Thinking you drywall over that corner but you may want to do both sides for balance. Or you get a mason in. The location of it is awkward and any decor placed over it will look like you were drunk when you hung it.

Any DIY faux brick will look awkward as the size and texture will never match.

A tall cabinet in that corner to cover it and start thinking about a redo for that wall. IMo the brick will never be matched and if changing this is in the future make life simple just cover it.

You'll have a hard time finding a brick mason to do such a small job. Go to Lowes or Home Depot and get some bricks and mortar and do it yourself after watching a couple of Youtube videos. Then paint to match.

Call a brick mason and have him steal brick from behind the TV to use in the open hole.

The raised hearth gives you a perfect starting point for drywall. Drywall from the edge of the hearth to the corner.