This is nothing more than a proof-of-concept and puts all rumors to rest of iOS 13 not being jailbreakable.
While we are not going to see the release of an iOS 13 jailbreak anytime soon especially since the OS is still in development stages, it is nice to know that it is possible to jailbreak it. Apple will possibly patch the exploit being used by @iBSparkes for the jailbreak in the final release of iOS 13. If not, we should probably see an iOS 13 jailbreak drop within a few weeks of the release of the OS in September or once iOS 13.1 is released.
— sparkey (@iBSparkes) June 11, 2019
If your iPhone is currently running a jailbroken build of iOS 12 – iOS 12.1.2, you should value it and stick to that setup. With Apple no longer signing iOS 12.3 or lower firmware, downgrading to a jailbreak-able firmware without having the required SHSH blobs is not possible.
As for the temptation to try out the iOS 13 developer beta, you should wait until its public release or until at least Apple gets around to releasing a few more beta builds. The current developer beta is too buggy and unstable and while the new features are enticing, they are not worth sacrificing your precious jailbreak.