I have fixed this twice without leaving, so it is worth trying before you go: partly because it might work and partly because it is a much better position from which to leave if it does not.
What actually worked:
Ask for a specific harder thing, by name. Not more challenge: the migration nobody wants, the system with no owner, the thing that keeps breaking. Managers are usually delighted; capable people volunteering for the hard unowned thing is rare.
Move internally. A different team is often a different job entirely, with none of the cost of leaving - you keep the relationships, the context and the tenure.
Take on something adjacent. Mentoring, hiring, being the person who does the thing nobody has done yet. This changes the shape of the week rather than the content.
Say the words out loud to your manager. Not as a threat, as a fact. I am not learning and I want to. A decent manager would rather solve that than replace you, and yours sounds decent.
Give it a defined period, a quarter - with something concrete agreed. If nothing changes in that quarter, you have your answer and you have it with evidence rather than a feeling. That is a much easier decision to act on.