Apple released for testing iOS 12.4 beta 4 with MacOS Mojave 10.14.6 beta 2.
These beta builds are completely separate from the current iOS 13 beta 1 and MacOS Catalina Beta 1, which are also in active beta testing for developers.
iOS 12.4 beta 4 probably focuses on fixing bugs and minor improvements for the iPhone, iPad and iPod touch, and no major new features or changes are expected (however, iOS 13 has many new features that will be released to the general public this fall) .
Anyone who is still registered in iOS 12.4 Beta can find the latest version of iOS 12.4 Beta now available using the Settings software update mechanism.
Likewise, MacOS Mojave 10.14.6 beta 2 probably focuses primarily on fixing bugs and minor improvements for Mac, and this release also doesn't expect any major new features or changes (but again in the next release of MacOS Catalina There are many interesting new features and are also associated with this fall).
Any Mac user still participating in the MacOS Mojave beta program will find that MacOS Mojave 10.14.6 beta 2 is available in the Software Update system setup.
Apple usually runs a few beta tests before releasing the final version to the general public.
The latest stable build of iOS at the moment is iOS 12.3.1 for iPhone, iPad and iPod touch, with the unique build of iOS 12.3.2 only for iPhone 8 Plus.
In addition, the latest stable build of system software for Mac is currently macOS Mojave 10.14.5.