Many managers have come up through the ranks; they are subject experts and promoted for that expertise as well as many other skills and strengths. If they received any L&D to support their promotion, being skilled at managing your boss was not part of that development.
Many do not have the confidence to communicate risks in connection with some of the decisions made by those above them, especially when those above are overworked, disorganised, disengaged or unrealistic in their expectations.
You can do the best you can, or you can manage upwards. Learn some tips and tools to help you do this.