The major visual update allowed users to switch the entire user interface to a dark theme.
If you are creating this for historical research, building a virtual machine, or restoring an old Mac, ensure you have a backup of the original 10.14 installer file, as it was removed from the App Store in 2021. What are you using this 10.14.b1 build for? Are you ? Are you trying to re-install it on an old Mac ? Are you developing software (testing against this old SDK)? macOS Mojave 10.14.b1 (18A293u)
Automatically organizes files on the desktop by kind, tag, or date. The major visual update allowed users to switch
Early beta users reported issues with the App Store, sometimes requiring users to sign out and back in. Are you
Introduced Gallery View, allowing users to browse files visually, along with enhanced metadata in the preview pane.
This was the final version of macOS to support 32-bit applications. Important Considerations (Historical)
Based on your query, 14.b1 (Build 18A293u) , which was released in June 2018. Key Features of Mojave 10.14 Beta (18A293u)