i made tutorial plane with winglets

They increase stability during turns slightly, and that is just because the game does not simulate lift from anything else than wings. IRL, the entire body of the plane acts in a way as a vertical stabilizer

They are useful in other aspects such as yaw stabilisers/dampers/side-force-generators. They can be used a bit like a polyhedral wing to have high roll stability

If anything happens, I'd assume they'd increase yaw stability. Other than that, it's likely nothing would happen, though someone will have to test that.

I don’t think the game simulates vortexes at the wing tips, so my guess would be no; winglets would have little to no effect on the stability of your plane.