The Legacy Product Graveyard: What’s a Product Owner’s job in a product with no future?

I'm considering my first Product Owner role, and it's for an end-of-life legacy product with a small team of developers. I don't have an engineering background, and I want to be a truly effective partner to the team. I'm hoping some of you who have been in this situation can give me a reality check.

The system is a complex beast with a lot of technical debt and extensive client-side customizations. There's no automated testing or user data to rely on. The company's long-term goals have shifted, so the development work isn't about new features, but purely about maintenance, stabilization, and migration to keep it operational for existing clients until it's no longer profitable.

I'd love to hear about your experience in a role or environment like this:

• From your perspective, what's the day-to-day like? How do you find motivation and keep morale up when the backlog is all technical debt? How do you feel about a non-technical PO making decisions on that kind of roadmap?
• What are the biggest frustrations? What does a PO do that makes your life harder, and what could they do to be a great asset in this kind of scenario?
• How do you find a sense of purpose and demonstrate value? When the primary goal isn't shipping new features, what makes you feel like the work is meaningful?

Any insights, anecdotes, or advice on how a new PO can best support their development team in a "legacy hell" environment would be incredibly helpful. I want to make sure I'm prepared for the realities of this job and that I can be the kind of PO that is an asset tho my dev's in this situation