How to add a tag in reactjs between two strings?

You should use JSX instead of string:

<div>No results.<br />Please try another search term.</div>

Because each jsx should have 1 wrapper I added a <div> wrapper for the string.

Here it is in your code:

render() {
   let data = this.props.data;
   let isLoading = this.props.isLoading;
   let isDataEmpty = Object.entries(data).length === 0;
   let movieList = isLoading ? <Loader /> : isDataEmpty ? <div>No results.<br />Please try another search term.</div> :
       Object.entries(data).map((movie, index) => <MovieTile key={index} {...movie[1]} />);
   return (
       <div className="movieList">{movieList}</div>
   );
}