Do you really want the steam client to have that kind of power on your PC? I sure don't. It's not like the machine is burning a bunch of power when it is just sitting there, doing nothing.

Microsoft won't let a user space app shutdown a PC and you shouldn't be running steam as an admin.

This can be at least a bit avoided with elevated subprocess started after you click "shutdown after download".

This way Steam will run in non-elevated mode, while subprocess waiting for the event from Steam client will have privilege to shutdown PC. It probably won't be very useful for PC, but might be for a laptops.

Isn't that what sleep mode is for when the system is idle?

Sure, why not some people do overnight downloads, and go to sleep, or gone out.

There is work around can always do using app that monitors your system usage, from CPU %, disk read, or writes, and etc... Which app shutdown your PC, and see below threshold you set over X period of time.

Another lazy method is using script to auto shutdown using countdown.

引用自 nullable：

Isn't that what sleep mode is for when the system is idle?

Yes, issue it may not always work, and could go to sleep during download which is rare as it can be due to either issue by OS, or app behavior.

But I assume OP want PC just off.

You can schedule your PC to turn off with a "Run" shutdown command, roughly some time after the download ETA is done, as long as it doesn't fluctuate too much.

Wouldn't be that hard to implement in the past some defrag programs and AV programs had that feature.

Shutdown is a simple command..... Steam could conceivably do that. My question becomes, why? Not like it burns a lot of power doing nothing....

And 'sleep'? Yeah. Win 11, box stock, wants to put your machine to sleep after 3 minutes of inactivity..... Which I think is just idiotic. When I am running updates, I don't want to babysit my machine for however long it takes. (and some of those updates seem to take FOREVER to download....) So, my machine NEVER goes to sleep, and most certainly never hibernates. It'll turn the screen off after an hour, but, that's it. (desktop.....)

10 years from now "hey i had this great idea and added it to steam"