Leave the laptop over my home theater receiver in the cupboard for days, and then pick it up and feel very warm?

What can happen there, the laptop was switched off for a long time in sleep mode, so only the display was folded down. I'm scared now that it's a new laptop. I've just picked it up and now I've noticed that it feels really warm, overheated. Is a new device. Can something happen there? I'm worried. Because it's a new laptop.

So if it is a new device, then the warranty applies.

To say something technically you had to know how you set up the laptop.

What does the laptop do - according to Windows - when it is closed?
This can be set separately for battery and mains operation.

Getting warm is generally not a problem. If the laptop gets too warm, the fan turns on.

I'm assuming that the laptop just turned off its screen and did NOT go into standby or sleep mode.

Screen was off but if it had been opened it would be directly on. It was in standby mode and had it in my laptop bag. And since I had a week's vacation I didn't use it and it was in standby mode for a week… Now worry me. Brand new 1200 euro laptop

Take a look to see what action is really set when closing the laptop in Windows.
The laptop knows several states between ON and OFF.
This goes through screen off, hard drive off, standby, hibernation (possibly hybrid) to 'completely off'.

If the laptop was noticeably warm in the bag - but not hot - then components (mainly CPU and RAM) were active and the energy of the battery was converted into heat.

Either way, nothing happens to the laptop…