How to cover up wall after removing a row of tiles to fit exhaust vent
Another way that could work well would be to remove the old tile setting cement and and grout left over by adjacent tile. Then source new tile that are cut to fit and install a row along that are set into new setting cement. Afterwards it could look almost perfect.

You would want to look at the tiles that you removed. Some of them may still be re-usable if they did not get all busted up when removed.