Nearly everywhere you first find an advisor, whether you have a topic in mind or not. In the US, at least, you first get accepted into a program and, only then, choose an advisor, and then a topic, with the advice and consent of the advisor.
In other places acceptance into a program begins with the advisor, but even then what you want to work on will most likely only be considered a suggestion to the advisor who may push you in some other direction.
I'd advise therefore that you find an advisor and explore what you want to do. They may have some specific things that align well with your hopes. But I'd also advise a bit of flexibility. Your dissertation has less effect on the trajectory of your career than you might suppose and you can easily change direction within a field after finishing a doctorate. A bit harder to switch fields, of course.
It is good, of course, to have some direction and to be able to express that desire. Choosing the final topic of research can be a bit of a dance with the advisor.