What should I build after learning the DevOps basics?

Pick a small app you already have and turn it into a deployment project. Containerize it, deploy it somewhere, then add a CI/CD pipeline and some monitoring. You don't need a huge application to make this worthwhile.

Once it works, deliberately break things and troubleshoot them. Try a bad configuration, a failed health check, a full disk, or a slow app. The useful part is figuring out what tells you something is wrong and how you'd recover.

A self-hosted app is another good option if you don't want to build the app itself. Pick one that interests you and has decent documentation, then use it to practice getting a container running and keeping its data available.

If you use a cloud trial, check the billing and usage pages regularly. Don't assume a trial means every resource you create will be free.

Stop collecting tools for a bit. You don't have to use Docker, Kubernetes, and three cloud providers in the same project. Start with one deployment, then add pieces when you have a reason to learn them.

For a different angle, The Phoenix Project is a novel about DevOps. It could be a useful companion to hands-on work if you want to think about the broader workflow as well as the tools.