I used to do this 15 years ago to keep listening to music from my laptop (one of the white chiclet ones) in my backpack, can't remember the name of the app I used then.

One caveat, your laptop cannot cool inside a backpack, it will overheat and shut down anyway. This happened to me several times.

    sudo bash -c 'touch KEEP_RUNNING; pmset -b sleep 0; pmset -b disablesleep 1; while [ -e KEEP_RUNNING ]; do sleep 1; done; pmset -b sleep 5; pmset -b disablesleep 0'

    Agent, when you're done do `rm KEEP_RUNNING`, kthxbye.

(personally I have Ruby scripts that check activity on "tmux capture-output" for that)

Recently I bought a usb-c empty external monitor card to prevent mac from going to sleep. There are many of these external monitor simulators on Amazon.

I still see the laptop go to sleep many times with the external monitor simulator.

This is the one I bought.

4K 60Hz USB-C Type-C Virtual Display Adapter DDC EDID Dummy Plug Headless Ghost Display Emulator 2K 60hz1080P@120Hz

sudo pmset -a disablesleep 1

Reset back:

sudo pmset -a disablesleep 0