Why is my Xbox series s overheating so fast when I have good ventilation and it's in a cold...

Looks like we would indicate a failed fan, it can't get rid of the heat fast enough just with radiation without it

It sounds like a vent to me and overheating.

I would think the same however it does it from a cold start so doesn't have time to get warm.

It's in a well ventilated area too.

Do you have it in a tv cabinet? If so take it out, my girlfriends Xbox 360 S was in a cabinet and it overheated very much like your console. You will need to put it in a better well ventilated area, hers now lives on top of the tv cabinet and has not overheated
since. The xbox 360 needs alot more than a few inches for ventilation.

It is definitely not a ventilation issue.

I cleaned off both the console and power pack which I do reguarly but it has a huge amount of space and it is always kept by an open window (it gets quite cold in here actually).

The console maintains a normal temperature.

This problem is also not followed up by the overheating error that I would get if it was overheating (which it has in the past hence why it has so much room)

If you do put your Xbox console into a cupboard, ensure that there is good ventilation to prevent overheating. If the cupboard is enclosed without ventilation then that raises the risk of earlier than normal failure due to overheating issues.

Good luck!