Apple released macOS Mojave 10.14.5 to fix a Boot Camp Fusion Drive bug. This update is for the iMac and Mac mini, as those two devices use Fusion Drives.
Fusion Drive Bug
Boot Camp is software that lets Mac users create a hard drive partition to run Windows. macOS Mojave 10.14.5 fixes a bug that prevented the creation of a new Boot Camp partition on iMac and Mac mini with a Fusion Drive.
The update can be downloaded from Apple’s support page, and not through the regular update channel in System Preferences because it’s only for iMac and Mac mini users.