Are you the real estate agent?

What is appropriate depends on the price range for the condo. The old tile will certainly look worse if painted over.

Remove that mantel iit looks silly and hang a great large piece of art there .

Modernizing the fp with micro cement does not work with the current fp. The current fp is not modern.

In order to use it, you would need to remove the mantel and build out a surround. That would be more expensive than tiling over the current tile that's on the surround.

I also think that the mantel looks odd - it's not connected to anything.

Here are examples of micro cement used on fireplaces:

Here are some others - they don't look as good as the ones in the above photos:

This one is the closest to the one in your photo - it is too traditional for this type of treatment.

The fireplace in your photo would look odd to just have micro cement troweled on the face of the existing tiles.

If this is for resale, it depends on what's usual for your area. If the condos at that price level are mostly dated, I'd just leave it alone.

If it needs to be updated to compete with other listings, popping off those tiles and replacing them shouldn't be that big of a deal. A marble or slate look with matching grout would look much better and wouldn't be that expensive.

If you go ahead with the tile, find someone to give guidance about the proportion. Not sure if the camera angle is the problem but the whole fireplace looks "off". Mantle, tile and hearth.

Agree to remove the mantle - what about seeing if a local stone yard has a stone remnant you could use? something uber simple like a black honed granite would be nice

Remove the mantle and paint and be done with it.