Apple has seeded the fourth beta of macOS Mojave 10.14.5 today. The release went to those developers registered in the developer beta program as well as those registered in the public Apple Beta Program. For both programs, to get the new update, go to Settings>Software Update on your Mac running macOS Mojave.
The releases of this beta comes a week after Apple released the third beta to testers. Like all of these betas of 10.14.5, there is not much in the way of new features. Instead, this release is very much focused on bug fixes, performance improvements, and security updates.
As Apple tends to do, we likely won’t know the full content of macOS Mojave 10.14.5 until it is released to the public. That release should happen in May. What is known is that it will not contain the new Apple TV app. Attention for that app has now turned to macOS 10.15 which is expected to be announced at WWDC in June. The Apple TV app for macOS will be based on Marzipan, making it much easier to have the app across iOS and macOS.
As always, both AverageAppleGuy.com and Apple do not recommend installing beta versions of Operating Systems on your primary or daily use devices in case you happen across a crippling bug.