This is working as designed per Microsoft Modern Standby.
I have this laptop Vostro 5490 since Oct 2019.  When I put my laptop to sleep for more than 10min, when I came back, I noticed the fan is still running....or it keeps running throughout the Sleep mode 1. Is this a normal symptom? 2. Does DELL laptops had different design fan concept? From the google research it mentioned;    PC enters a low-power state. The PC's state is kept in memory, but other parts of the PC are shut down and won't use any power. When you turn on the PC, it snaps back to life quickly—you won't have to wait for it to boot up.10 Jul 2017> If I put the laptop to hibernation mode, the fan will be OFF. Best regard,
Fan still running at Sleep mode