Hi Bayram,
Based on Microsoft's published information, KB5087066 was published to WSUS metadata and is not a Catalog-only update. The official KB article explicitly lists Windows Server Update Services (WSUS): Yes under "How to get this update," which indicates that Microsoft intended the update to be available through WSUS synchronization.
One important detail is that KB5087066 is a .NET Framework cumulative update for Windows 10 version 1809 / Windows Server 2019, not an operating system cumulative update. Microsoft notes that this .NET update is installed "by applying the operating system update" and is classified as a Security Update.
Since WSUS synchronization completes successfully, other updates are syncing normally, and wsyncmgr.log contains no reference to KB5087066, this suggests that the update metadata is either being filtered before synchronization (product/classification/language settings) or is no longer being offered to your WSUS configuration despite remaining available in the Microsoft Update Catalog. The fact that it is still downloadable from the Catalog does not guarantee that it is currently being synchronized into every WSUS environment.
Given the evidence, I would not conclude that KB5087066 was withdrawn from Microsoft Update, because the official support article still states WSUS = Yes. Instead, I would recommend reviewing the WSUS synchronization settings for Windows 10 Version 1809, Windows Server 2019, and Security Updates, and if those are already enabled, opening a Microsoft support case so the backend publishing status for KB5087066 can be verified. Based on the publicly available information, the update appears to have been published for WSUS synchronization.
Harry.