I am thinking about self hosting gitlab. Doing some good stuffs with it like branching, merging, gitlab ci/cd etc. Then work with docker containerize real applications. For that I will also have to learn some spring boot (I want to work with Java apps). Terraform to initialize clusters and virtual machines. k8s for further containerization. Then some monitoring tools like prometheus, grafana. Finally learn to use cloud.

Likewise, you can do hands on on data and logs processing using elk stack.