std::chrono::year_month_weekday_last::ok
From cppreference.com
                    
                                        
                    < cpp | chrono | year month weekday last
                    
                                                            
                    | constexpr bool ok() const noexcept; | (since C++20) | |
Checks if this object represents a valid date. Since a year_month_weekday_last represents the last weekday of a particular month, it is valid as long as the year, month and weekday are valid.
Return value
year().ok() && month().ok() && weekday().ok()