This new beta generally focuses on fixing the past errors and making it more stable rather than adding new features to it. Apple has also shared a release note where it mentions what has changed on macOS 10.14.5 beta 4 which can be found below.
WHAT’S NEW IN MACOS 10.14.5 BETA 4
Copy-protected video content plays back correctly on iMac Pro. (49174801)
The Accessibility Events switch was removed because related aspects of the W3C AOM effort are no longer applicable. (49784417)
Date and Time
Support for the Reiwa (令和) era of the Japanese calendar, which begins on May 1, 2019, is now available. The first year of Japanese-calendar era is represented as “元年” (“Gannen”) instead of “1年”, except in the shorter numeric-style formats which typically also use the narrow era name; for example: “R1/05/01”. (27323929)
Kernel extensions signed after April 7th, 2019 must be notarized in order to load on macOS 10.14.5. (50016570)