On the whole, it is not very helpful. Junior high school emphasizes geometry and senior high school emphasizes algebra. Senior high school mathematics knowledge is useful for junior high school questions in the following aspects:

Sine theorem and cosine theorem (knowing any three values of the sides and angles of a triangle, you can solve all the values of the whole triangle, and of course there may be two solutions, such as knowing the edges and corners), which may be the most useful knowledge.

Analytic geometry turns all geometric problems into pure algebraic calculations, but it is usually many times more complicated than geometric methods.

Plane vector transforms some geometric problems into vector calculation, but it is rarely used.

Generally speaking, high school mathematics is not helpful to junior high school mathematics, but it is related. After all, high school mathematics is based on junior high school mathematics.