Systems engineers need a combination of management and technical skills.
Computer systems engineers need expertise in software design and implementation, agile software delivery, programming in different languages (at least one high-level language like C is highly recommended), cloud-based solutions, virtualization, networking principles, data safety, and more.
Depending on your specialty, you might need additional tech skills. For instance, experience in cloud environments like AWS and Azure is likely not a must for transport systems engineers. It is, however, virtually indispensable for networking professionals.