Is it possible to execute a code in runtime when gets updated over the air (OTA)?
On many Arduinos the processor is only a few dollar part.  You are asking for a feature that only starts appearing on platforms where the processor is over an order of magnitude higher in price.  Further, such inexpensive processors normally run a single program.  Running a sketch while managing a download &amp; update would best be done by two programs existing in an operating system.  Again, likely requiring a processor an order of magnitude higher in price.

Instead, consider implementing your design using two different Arduinos.  Swapping one out for the other after updating.   Hot swapping may not be trivial.  This really depends on how your application interfaces with the world. But likely will be much easier than solving the problem of designing the supporting software to make sketch updates transparent to the Arduino user.