Meaningful research in PhD with no publications

Your situation hints at a mismatch between your supervisor's supervision style (which is fairly hands-off) and the style you would need to be productive (which requires more guidance and input in the beginning, with the goal of ultimately having you become more independent).

My recommendation is: Find a co-advisor with a more hands-on supervision style. That could be somebody in your group who is fairly productive (most likely a postdoc, assistant professor or young associate professor), with a visible publication track record. Most people who are that way have more problems to work on that they can solve on their own. You should have your main advisor on board with this, which might be easy to achieve, since advisors have an active interest in seeing their students graduate.

I don't want to step on the excellent answer of lighthouse keeper but an additional idea would be to join or form a discussion group in which a few students, perhaps in a similar situation as yourself, get together to discuss issues and search for open questions. Read a few papers (jointly) and discuss them. What is left unsaid in the papers.

The synergy of a group, if like-minded, can be helpful.

And a group can transform into a collaboration group over time. This can be valuable in its own right.

I like reading about new solutions, new problems and try to solve them myself.

Do you find any flaws in the solutions that you read about? Any space for improvement? Could a different approach be taken?

Are the problems you read about framed appropriately? Maybe they are too theoretical, and making more realistic assumptions would yield different results? Maybe the problems are defined in a too specific manner? Could they be generalized for some benefit?

Start thinking critically and soon you will find plenty of ideas which are publish-worthy.

You can start by nit-picking, finding even small issues in the published works, looking for a hole. Then, you can try a higher level approach, like asking yourself questions why nobody has tried to do something in a specific way, or why some problem has not been tackled in a rigorous manner.

Do not treat published material as some form of revealed truth. You need to believe in yourself. Believe that you can do just as good as your peers (not the other students, but the other researchers which publish), or even better. Basically think of yourself as a researcher, not much as a student. Doing PhD is a (hopefully paid) job, not a school!