I think a polite ask is the best option. Many don't know they are doing it.

Heres the thing. .people are allowed to talk or have conversations at a normal volume on planes. that isnt something the FA would stop people from doing. This passenger is by themselves, but it seems like that same should apply?

The scenarios I run into much more frequently is someone watching or listening on their phone with the volume on (no headphones). I find that super irritating. And there if it bothers me, I would mention to the FA as it is against policy.