Apple has released a supplemental macOS 10.14.5 software update, the update is available for some models of Apple’s Mac computers.
The update is available for trhe 15 inch MacBook Pro that comes with the T2 security chip and it fixes a firmware issue on the notebook.
You can see the release notes below, there does not appear to be anything else included in the update:
The MacBook Pro Supplemental Update addresses a firmware issue affecting 15-inch MacBook Pro computers with T2 Security Chip, and is recommended for all users.
If you own the 15 inch MacBook pro with the T2 security chip then it is recommended that you install the latest software update, you can do this from the App store or the Apple menu on your device.
Source 9 to 5 Mac