According to Apple page https://support.apple.com/en-ca/HT201475
requirements for Mojave exclude you 2011 Mini.
You can upgrade to macOS Mojave from OS X Mountain Lion or later on any of the following Mac models. Your Mac also needs at least 2GB of memory and 12.5GB of available storage space, or up to 18.5GB of storage space when upgrading from OS X Yosemite or earlier.
MacBook introduced in early 2015 or later
MacBook Air introduced in mid 2012 or later
MacBook Pro introduced in mid 2012 or later
Mac mini introduced in late 2012 or later
iMac introduced in late 2012 or later
iMac Pro (all models)
Mac Pro introduced in late 2013, plus mid-2010 or mid-2012 models with a recommended Metal-capable graphics card.
To find your Mac model, memory, storage space, and macOS version, choose About This Mac from the Apple () menu. If your Mac isn't compatible with macOS Mojave, the installer will let you know.