Product Managers should involve Product Designers and Engineers as early as possible in the product development process (problem discovery, solution shaping, e.g.)
Involve Product Designers earlier so that they can challenge you to build a more friendly and user-centric solution.
Involve Engineers earlier so that they can challenge you to build a more concrete solution, a more scalable system, etc.
This also helps generate more ideas, create empathy, and increase team engagement.
P.s: However, it may be premature to involve them if you don’t yet have a use-case or a clear understanding of the problems you’re trying to solve. The sweet spot is to include them early enough so they can grasp the context, but not so early that they become overwhelmed, taking into account their expectation, skills and interests.