Apple today seeded the third beta of an upcoming macOS Mojave 10.14.5 update to its public beta testing group, a day after seeding the beta to developers and two weeks after releasing the second macOS Mojave 10.14.5 public beta.
The macOS Mojave update can be downloaded using the Software Update mechanism in the Mac App Store after downloading the appropriate profile from Apple's beta testing website. Apple's beta testing site gives users access to iOS, macOS, and tvOS betas.
We don't yet know what improvements the macOS Mojave 10.14.5 update will bring, but it likely focuses on bug fixes and performance improvements for issues that weren't able to be fixed in the macOS 10.14.4 update.
There were no notable features found in the first three developer betas of macOS Mojave 10.14.5.