Do you run your own server/VPS? If you are looking into backend development I can highly recommend running your own, and setting up things you're interested in, stumble over, or find useful.
I've gained a lot of experience through working on what interested me, I found useful, or needed, and setting them up on my server too.
Do you not have things you stumble over or tools you would find useful? Or FOSS you use?
I've made tools for myself for file checksums, for practicing things, for storing resources/information, for publishing and integrating my services, for visualization and debugging, for parsing data formats, for cutting video, for downloading and converting things, and many more.
If you are looking into backend specifically, what kind of backend? For what kind of service or application?