Why does my still Mac sleep when closing its lid?
In order for your Mac to stay awake while in clamshell (closed lid) mode, you must meet very specific requirements set by Apple. You can review those requirements here:
Why Can't Amphetamine Override This?
Any claims made by an app from the App Store regarding being able to keep your Mac awake while the lid is closed and not meeting Apple's requirements are either 1) false, or 2) from an app that existed in the Mac App Store prior to Apple's sandboxing requirement going into effect back in March of 2012.
Even if #2 is true for an app, you should remain skeptical before purchasing an app from the App Store that claims it can do this without meeting Apple's requirements. The only way to override the default behavior of a Mac sleeping when its lid is closed (and not meeting Apple's requirements) is to modify macOS through a kernel extension, or by running a command as the root user. Neither of these can be done by an app distributed through the Mac App Store.
That said, it's possible Apple's App Review team messed up and let an app that does something it shouldn't be able to slip through the review process (it's happened before). If this is true, however, make sure you really trust the developer of the app. Root user access is not something to take lightly or be given out freely.
Amphetamine did not exist in the App Store before Apple's sandboxing deadline in 2012. If you search the internet for Amphetamine for Mac reviews, you'll find some people have claimed that Amphetamine can keep your Mac awake while its lid is closed no matter what. Even some of Amphetamine's App Store reviews state it can. Unfortunately, that's not the case. Simply put, Amphetamine should not be able to override Apple's requirements for clamshell use of your Mac. Apple does not allow it. If it were allowed, certainly, the feature would be added to Amphetamine. It's a popular request! :)
Ok, that's all fine and well, but it doesn't solve my problem
There are some potential options, a few of which are listed below. Note that none of these other apps are affiliated with Amphetamine or its developer, William Gustafson. I, William Gustafson, have never used any of the following apps or commands on my Mac, and cannot troubleshoot any issues they create on your Mac.
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