One topic that has become very fashionable is Artificial Intelligence (AI). Having a good knowledge and understanding of AI will certainly stand out when applying for jobs.
You could research existing algorithms and write your own implementation, being especially careful to optimize it for whatever goal you have decided to implement in your program.
Or, alternatively, you could choose to use one of the existing AI services and write a front-end to interact with it. For instance, you could write a program to gather data, then train a Model, and then send queries to the model.
The ability to do this is in high demand, so demonstrating knowledge in this topic will help you a lot when applying for a job in this area.