https://wccftech.com/windows-10-version-2004-is-now-on-one-quarter-of-windows-10-pcs/

Microsoft released Windows 10 May 2020 Update, version 2004, at the end of May. Despite being baked in the Insider rings for a long time, the new version of the desktop operating system came plagued with several known issues, that pushed the Windows maker to deploy multiple compatibility and safeguard holds.

On one hand this stopped those who wanted to upgrade to the latest version from getting it and then it didn't give other Windows 10 users the confidence on this version to make the upgrade decision. However, things have started to improve now that the Windows maker has managed to fix most of the known issues through the past two cumulative updates.