The only way I found to copy the db into the user dir (godot 4.3)
var db_file_content : PackedByteArray = FileAccess.get_file_as_bytes("res://data/data.db")
var file : FileAccess = FileAccess.open("user://data.db",FileAccess.WRITE)
file.store_buffer(db_file_content)
file.close()