There is no such thing. Volume and display settings are controlled by three buttons at the top on the left side of the display.

https://www.dell.com/support/kbdoc/en-us/000182112/inspiron-24-5400-5401

These are the only available keyboard shortcuts for this model.

you may use shortcut to switch to external display monitor, but none to switch from pc to hdmi-in as display only.

How can I switch to HDMI input as display only?

The button on the case does that and only if the pc is working. It doesn't let you use the AIO as a monitor when the hard drive and os are dead.

I understood. Thank you.