std::chrono::utc_clock::from_sys
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   template< class Duration > static std::chrono::utc_time<std::common_type_t<Duration, std::chrono::seconds>>  | 
(since C++20) | |
Converts a sys_time t to a utc_time u that represents the same point in time.
u.time_since_epoch() - t.time_since_epoch() is equal to the number of leap seconds that was inserted between t and 1 January 1970. If t is the exact date of a leap second insertion, that leap second is counted as inserted.
Return value
A utc_time representing the same point in time as t.
See also
|    [static]  | 
  converts utc_time to sys_time (public static member function)  | 
|    (C++20)  | 
  convert time points of one clock to another  (function template)  |