Soft power is simply the capability to persuade others without coercion. So it’s usually a much less destructive tool to achieve the same goal when the alternative is “hard” power.

Whether you build the soft power ethically or unethically (and false propaganda could be one of the many unethical ways to build soft power) is upto the country in question.

And whether that soft power is deployed for “good” or “bad” purposes is also dependent on the actions and goals of the nation.

So it’s kind of as meaningless to ask whether soft power is “good” or “bad” as it is to ask whether a hammer is good or bad, except generally “soft” power tends to be a better way to achieve the goals of a country than the alternative (which involves the threat and/or actual dropping of bombs) and the methods of developing soft power tend to generally be better than the alternative (distributing medicines for Thberculosis, cultural exchanges, etc instead of building a bigger and more dangerous military).