Clone a wakatime, potential for 10K+ users, will you choose MongoDB, PostgreSQL, or DynamoDB?

Wakatime https://wakatime.com/ is a fun service that tracks how much time(seconds) you spend on coding and which files, it has historical dataset, views on analysis on what language you mostly working and a global leader board.

If I want to design an architecture to clone wakatime and potential for 10K+ users, can you guys share what’s the thinking process on choosing the Database and why?

Thank you!