Dell P2723QE 27" 4K UHD USB Type-C Hub Monitor - Manual (Page 35)

Setting up the monitor │ 35
3. Go to System Settings .
4. In the drop-down menu of When I press the power button , there are a few
options for selection namely Do nothing/Sleep/Hibernate/Shut down , and
you can select Sleep/Hibernate/Shut down .
NOTE: Do not select “Do nothing”, otherwise the monitor power button will
not be able to sync with PC system power state.