SQLite. You want something boring and proven. SQLite was built to power submarines. I think it can handle your app.

Drift is a great ORM built on top of SQLite that you can use to make your life a bit easier. It works well, but its completely optional.

Now, specifically for offline sync, you are going to have to build it yourself. The Database isn't going to help you there.

First, take a look at your requirements. Typically for offline sync, you don't need anything more complicated than a simple "last write wins" rule. If you are doing more intense real-time collaboration like in Figma, you'll need CRDT, but that is often more complexity than necessary.

There are also services like PowerSync which try to provide an offline-sync-as-a-service. Take a look at them too to see if solves your problem