No. Anybody can have such an idea.

No publisher in the research field is interested in untested hypotheses. All hypotheses must be tested before they will be accepted for publication.

What you can do is publish a critical review of the work already done to show that it needs research work.

Within ResearchGate, if you click "Add New" and then select "Other" you can enter a research proposal or thesis...and then ask for feedback.

This is not the same as a peer-reviewed journal publication, and probably would not be persuasive for promotion and tenure, but it at least documents your idea and may provide some feedback.

Is there a way to publish a hypothesis?

Agreed with Ian that you can consider writing & publishing a review article with untested hypotheses at the end / at conclusion section prompting readers for future research recommendation.

However, merely doing above might give away free ideas to others to embark on an empirical research. Why not consider - continue your empirical research so that your hypotheses are tested with empirical findings and publish your article in parts or as a whole?

Keep it secret in your research notebook with every entry dated.