I'm trying to make my first API with an accompanying website, and I'm using tutorials. I decided the MERN stack was the way to go, since it seemed popular and easy.

I have some experience with SQL itself, but have never connected a database to an actual application.

So I got to the point of making my database in mongoDB when I saw some stuff about how mySQL is more secure than noSQL, and how noSQL has some disadvantages.

The api/website I'm making is just a pet project, but if it ever does become popular, would I have to move my databases? Or is this a "cross that bridge if/when I get there" situation?

Alternatively can I have the same database in multiple places at once? As in, bot mySQL and noSQL?