I’m assuming that the model number is ME16K3000AS/AA.
It seems as though there may be a problem with the control board, given that the light and the turntable both don’t work.
I can’t find a schematic for the board but have found a schematic for a similar Samsung oven and the power supply to the different components is provided by individual relays operating on the control board. Hopefully this is similar to your model.
As the magnetron power supply is also provided by a relay operating on the control board and you said that the oven is heating, this proves that power is available on the board.
Is the fan working, you never said?
Check the control board and see if there is a relay marked Main. This relay supplies power to the fan, the main light and the turntable via their respective relays on the board. The magnetron power is not supplied through this relay. It has two relays marked Power High and Power Low
It may be that the individual relays are operating but there may be a problem with the Main relay or its contacts.
The main light is operated by a relay marked Vent low which also supplies the fan but there are more Vent relays to control the fan at higher speeds. The turntable relay is marked T/table.
Be safety aware when working in a microwave oven. The HV capacitor can store >5000V DC for months even if the power has been disconnected for this length of time. This amount of voltage can cause serious injury or worse. The HV capacitor needs to be correctly discharged as soon as it is accessible after removing the cover from the oven and before performing any testing or repairs. If you don’t know how to test safely when working in a microwave oven, then don’t do it! It’s not worth it.