Most of the time I only use my 2016 Fortuner in the city and only on few occasions I use it to go to province. Now since city driving is what I am used to, there were some occasions where going to the province ang cruising around 100kl/h, I forgot to turn off the engine only after 5 mins or so and instead turned it off immediately. Would this destroy my engine?

I would say that before I reach the destination and turn off the engine, I would slow down (but still running around 30-40kl/h) for about 20-15mins or so... would that be any consolation and consider the engine as having cooled off during that slow down?

I am a noob here...