What Database and server should I use for my app?

I need to build a project for my final year. I and my team have figured out the abstract of our app i.e, we will be building an E-learning app and website focused on covering the basics of computer science targeted for students of age 12-15. We will be integrating the Active-learning feature as well, using which we can give personalized tests and content to each student.

Technicalities:

• Python/Flask – For Backend(Algorithms and ML)
• React – For Frontend(React because we want to build both app and website)

I needed help deciding which Database I should use, It should be accessible by cloud and I'm not sure about how do I host it as well. I would need around 10-15GB of space and would be great if it is free. All the projects I have worked on previously had MySQL as dB on the local system only. If I could do something similar and make my system only as host for processing and DB also works. But preferably on a hosted server. How do I go about this?

Thank you