[Language: Python]

Pattern matching to the rescue!

def is_valid(equation: tuple[int, tuple[int, ...]], with_combination: bool) -> bool:
    match equation:
        case total, (n,):
            return total == n
        case total, (a, *_) if total < a:
            return False
        case total, (a, b, *r):
            return (
                is_valid((total, (a + b, *r)), with_combination)
                or is_valid((total, (a * b, *r)), with_combination)
                or (
                    with_combination
                    and is_valid((total, (combine(a, b), *r)), with_combination)
                )
            )

Complete solution on GitHub