https://www.bleepingcomputer.com/news/microsoft/windows-10-insider-build-18875-released-merges-fast-and-skip-ahead-rings/

Microsoft has released Windows 10 Insider Preview Build 18875 for Insiders in both the Fast and Skip Ahead rings. With build 1903 already released to Insiders and publicly being released in May, Microsoft has merged the Skip Ahead and Fast rings so that they are both now receiving the same 20H1 builds.

The only updated feature in this build is the availability of a new Japanese IME that is more stable and secure than the previous one. Otherwise, this build is just a bug and maintenance release.