As @vladaad stated drives don’t come with the OS installed you need to install it your self.
There are a couple of ways to install a fresh OS with very little effort! If you have a good internet connection you can install the OS via Internet recovery just by connecting your system to either a WiFi or Ethernet connection.
If you have access to a second system you can setup your Mac Mini in Target Disk Mode and using a Thunderbolt cable between the two systems you can use the other Mac OS installer to install the OS onto your Mini.
Another way is to get a USB thumb drive and set it up on the other Mac or before you remove your current drive set it up as an OS installer.
So how do I do all of these different ways? Here you go!
Internet Recovery - Restart your system and press '''Command (⌘)''' and '''R''' keys
Target Disk Mode - Restart your Mac Mini system and press '''T''' key, then connect your other system to yours via Thunderbolt Cable.
Setup a bootable OS installer follow this guide [https://www.macworld.com/article/3284378/how-to-create-a-bootable-macos-mojave-installer-drive.html|How to create a bootable macOS Mojave installer drive]
And here’s how to get the best macOS for your system [https://support.apple.com/en-us/HT210190|How to upgrade to macOS Mojave] (jump down to Step 4 for the direct link) Use this OS for either method.
'''References:'''
-
[https://support.apple.com/en-us/HT204904|How to reinstall macOS from macOS Recovery]
[https://computers.tutsplus.com/tutorials/understanding-the-applications-for-target-disk-mode--mac-60609|Understanding the Applications for Target Disk Mode]
+
* [https://support.apple.com/en-us/HT204904|How to reinstall macOS from macOS Recovery]
* [https://computers.tutsplus.com/tutorials/understanding-the-applications-for-target-disk-mode--mac-60609|Understanding the Applications for Target Disk Mode]
As @vladaad stated drives don’t come with the OS installed you need to install it your self.
There are a couple of ways to install a fresh OS with very little effort! If you have a good internet connection you can install the OS via Internet recovery just by connecting your system to either a WiFi or Ethernet connection.
If you have access to a second system you can setup your Mac Mini in Target Disk Mode and using a Thunderbolt cable between the two systems you can use the other Mac OS installer to install the OS onto your Mini.
Another way is to get a USB thumb drive and set it up on the other Mac or before you remove your current drive set it up as an OS installer.
So how do I do all of these different ways? Here you go!
Internet Recovery - Restart your system and press '''Command (⌘)''' and '''R''' keys
Target Disk Mode - Restart your Mac Mini system and press '''T''' key, then connect your other system to yours via Thunderbolt Cable.
Setup a bootable OS installer follow this guide [https://www.macworld.com/article/3284378/how-to-create-a-bootable-macos-mojave-installer-drive.html|How to create a bootable macOS Mojave installer drive]
And here’s how to get the best macOS for your system [https://support.apple.com/en-us/HT210190|How to upgrade to macOS Mojave] (jump down to Step 4 for the direct link) Use this OS for either method.
'''References:'''
[https://support.apple.com/en-us/HT204904|How to reinstall macOS from macOS Recovery]
[https://support.apple.com/en-us/HT201255|Mac startup key combinations]
[https://computers.tutsplus.com/tutorials/understanding-the-applications-for-target-disk-mode--mac-60609|Understanding the Applications for Target Disk Mode]