In addition to what is above, there is a way to skip over NPCs to see if they are able to be interacted with (instead of getting a generic line from them once in talking to them). When you hover over them, your mouse icon will turn to a speech bubble.
When in new areas and I want to make sure I interact with all NPCs I’ll just run my cursor over the NPCs to see which ones I can talk to. Probably the closest you’ll get to an icon over them showing they can be interacted with.
Thank you for this tip
I always play on action camera so I never noticed this.