Mobiles and desktops

[ghost]

You could use the golang version of leveldb and expose it as a dart plug-in.
It's quite easy to do and others are also writting flutter plugins to wrap golang.

The golang leveldb is well used also these days.

https://github.com/syndtr/goleveldb

To compile for mobiles everyone usses gomobile bind.
Then you need to write the binding code for iOS and Android.

The level db API is not many method calls ?

There are many examples I could send you if you want