For this example, the mass (m) is 0.604 kg. It can also be calculated in AIM using result type as "Calculated value"
The Specific heat (Cp) from the Material properties is 434 [J kg^-1 C^-1] (and not 0.434 which you have used in your calculation. Since the unit of mass is in Kg, we need to use the value of Cp with similar units.
The initial and final temperatures are 22 deg C and 800 deg C respectively.
So using the equation Q = m*Cp*deltaT, we get the value of Q as 204011.3643 J. Or if we convert this value in Watts, it will be 204011.3643 W (J/s). So this much energy or heat is required for the cylinder to raise the temperature to 800degC in 1 second.
Coming back to your problem where the time taken to raise the temperature is 4 sec, that means you need to specify 204011.3643/4 = 51002.8411W in the Heat Generation panel. See below snapshot. This value is closer to what you have already specified (50000W). So this value (Q) is the one which you are specifying as an input in simulation and it is not something which you want to see it as a result output.
Using above value, if you now solve the problem in AIM and check the temperature value, you can see the final temperature as 800 degC. This value matches with the value that was specified in the equation. This validates the results from simulation and the equation.
Regarding the heat flow result, it's value is 0 because there is no flow of heat within the body. And this value is not equivalent to the energy (Q) value. If you check the temperature contour, the temperature is uniform everywhere.