You can actually use command line to update your Mac to the latest macOS release. It's much faster than the usual Mac App Store route.

Using Command Line to Update Your Mac is Far More Efficient - Lets You Use Your Mac During the Update Process

Updating a Mac to the latest macOS release might seem exciting, but it's a painful process to go through. First, the update is downloaded, then installed, and during the installation process your Mac is rendered absolutely unusable. A bit of a disappointment if you're asking me.

Thankfully, you'll be surprised to learn that you can use command line to download and install macOS updates. Why would you wanna do that? Because during the installation process, your Mac is completely usable, and the only restart that is required does not take more than a couple of minutes. Sounds like something you would root for, right? So, without further ado, here's how it's done, according to Reddit user microbug_:

Updating macOS through the App Store can take a very long time — for me it's typically around 30 mins of rebooting and waiting.

macOS has a built in softwareupdate utility, which is much faster. It also allows you to use your Mac while it updates (the updates seem to be applied while it's powered on, and the reboot takes much less time than if it's triggered by an App Store update).

To use it, open Terminal and run one of the following commands:

softwareupdate -l to list available updates

sudo softwareupdate -i <name of update from the above command> to install one specific update

sudo softwareupdate -i -a to install all available updates

I usually do softwareupdate -l to check for updates and softwareupdate -i -a to install them.

To give a rough time estimate, it took around 10 mins to install the latest version of macOS 12.6 just now, and my MacBook Pro was only unusable for about 2 mins while it rebooted.

Apple released the macOS Sierra 10.12.6 update just yesterday. And it's best you try this method right now rather than later. Besides, if you've been holding back just because macOS takes way too long to update, then your prayers have been answered in the most prompt manner.