After a year of using mongo in prod and personal projects I have realised some things. Its really nice early on the project, especially when there are changing requirements and for small projects or proof of concepts.
But when you make commercial software things tend to get more complex and relational. Stakeholders want reporting and even a report building which a document store isn't the best at.
With most projects projects when they get big things get relational and this becomes more and more expensive to handle in terms of compute power and developer time.
I don't doubt mongo has its place, maybe as an secondary specialised data store or if the project is inherently document oriented.
Blog over.

I hate the company (agency) I moved to...I've negotiated good pay and the project for cutting edge medical product which will change the world (cancer diagnose and it actually works).

Now the dark side I've got shit tier laptop which I don't want, overtime is payed 30% less, all the people in the agency from development team don't know shit and are mostly I would call them juniors (of course who would with enough seniority work with shit hardware and almost not payed overtime), only tap water and since this is the old part of town you instantly get sick, they treat people like shit.

The product dark side. We are actually working on crm for doctors to input patient data, we cannot have any real data because we are the agency people, product is being led by the guy who has 0 production experience (they choose the database basically with coin toss and emulated the mongodb in postgress with jsnob, they don't know how to build their own auth system hence my previous rant about b2c, they are using cognito and now moving to auth0 which probably won't fit their need because a lot of stuff needs to be custom), they are choosing every hipe tech out there without any prior experience. It's chaos...

I'm trying to guide them but i think this will be a huge expensive failure and that i need to leave asap.

There I feel better now, moral of the story, choose startups wisely.