Dell P2723DE 27" 1440p USB Type-C Hub Monitor - Manual (Page 46)

46 │ Setting up the monitor
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.
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.