Firebase or Express+Mongo?

Question

MongoDB

I am planning a project - the front on Nextjs, the question is how to implement the back.
There will be no complex logic, in fact it will be used only as a database, I think how to implement it - write your back on express + mongodb or use firebase?
With express and mongo, there is experience, how things are going with firebase - is it safe when used from the front, it usually seems to take place in mobile applications