https://wccftech.com/windows-10-preview-build-19645-is-out-for-insiders/

Microsoft has released a new Windows 10 Insider Preview Build 19645 to those in the Fast ring. Similar to the last several builds, today's release also doesn't bring anything new focusing entirely on general improvements and bug fixes. Microsoft is likely to begin working on Windows 10 2021 (codenamed Iron) later in June.

But until that happens, here is what's improved with Windows 10 Preview Build 19645: