What’s the usual security concerns/measure around databases when developing an app (consider amateur apps etc. too) Other than looking at OWASP vulnerabilities, curious of the more practical application of securing.

So I've been dragging my feet developing an app and to avoid the major security risks I'm leaning towards local storage using SQLite. However, I'm really keen on making the application cross-platform and with the ability to share information with other users.

However, I'm hesitant to use online storage and databases as I've never been able to find a practical explanation of how to implement security measures. To make this absolutely clear, take this for example, just an example:

"Do I code defenses against SQL Injections on EVERY SINGLE piece of SQL code?"

Also, being new to security, wouldn't the system be an easy target?

Back to the question… How do these amateur apps that you see on app stores do it? Do they throw caution to the wind and just do whatever without security measures or am I just overcomplicating it?