I built a web app that looked very similar a few years back: friends & family collaboration on a trip plan, itinerary with map view, packing list, notes/journaling, favoriting, private or public with commenting, that sort of thing.
My thesis was that the current common method of trip planning in a shared doc was messy, and a more structured, guided approach would make the process easier for users. And being able to share/show trip plans with others who aren't on the trip would be something people would want to do.
My goal was to scale it and get actual broad adoption, make it a social experience, but even getting a handful of users was an uphill battle.
I found that my thesis was likely wrong for a couple of reasons:
1. The messy shared doc approach had the benefit of being very low-friction. It's easier to just type a bulleted list than to click "add item" and fill out some form fields.
2. Browser usage was (I think) a limiting factor. I'm not sure if it would have worked as a native mobile app, but it definitely wasn't going to work as a web app.
3. When people want to show off their trip or look for travel inspiration, they turn to apps like Instagram and Tiktok. They want visuals with photos/videos, not a list with a map. It's very difficult to create a new purpose-built social network.
I ended up winding it down and moving on.
I don't mean this to be a Dropbox "why are you building this" comment, but more hopefully pointing out a few challenges that exist in the space that you'll likely need to think about if you want to scale.