I supervise a final year project module comparable to a Dissertation. Early in the module, students are required to come forward with ideas. Some students struggle to come up with one idea, others arrive with ten. In the case of the latter (which sounds similar to you), I would send them off to shortlist to 2 or 3. TBH the whole ten would rarely be equally suitable in any case and so I would want to see that the student could use their critical judgement to pick the strongest ideas. If you have a tendency to keep openng up new ideas, narrowing down and making a decision will probably be hard for you. So perhaps you could make the decision based on the following:
- what is the most "do-able" idea - the one it will be "easiest" to undertake and complete? (it's often best to avoid subject areas that have major challenges such as ethics, access, etc)
- what is the most useful to you future career?
- which one interests you the most?
As others have said, you really need to go back to your supervisor with a viable shortlist.