The most recent Android 10 beta that was released for the Galaxy S10 and Galaxy Note 10 broke a very important functionality: support for Samsung DeX on Windows and Mac. Samsung had said that a beta version of DeX for PC would allow S10 and Note 10 owners on the Android 10 beta to use their phone with DeX on a PC, and that beta DeX for PC app is now available for download.
Samsung suggests uninstalling the previous version of DeX for PC before installing the new beta release; we can confirm that the beta app does work with the latest Android 10 beta on both the Galaxy S10 and the Galaxy Note 10. Whether Android 10 brings some new DeX functionality on Windows and Mac PCs is something we'll have to wait and see, as Samsung hasn't said anything yet other than the fact that the existing DeX for PC app doesn't work with the latest version of Android.
Download the DeX for PC beta app from these links: Windows 7/10 | Mac