How can I fix Windows Server 2019 update error 0x80073701?

The log excerpt is useful: 0x80073701 is ERROR_SXS_ASSEMBLY_MISSING, and the failure occurs while CBS is resolving an assembly. Check CBS.log and DISM.log around the first failure, not only the final error. Also confirm that the server is actually Windows Server 2019 build 17763, that there is enough free space, and that no interrupted servicing operation is pending. If repair with matching media and manual servicing-stack updates still fails, an in-place repair upgrade using current Server 2019 media may be safer than deleting component-store files.

The CBS entries indicate that a required side-by-side assembly is missing, rather than a simple Windows Update cache problem. Since the server has been behind since 2021, first review the full CBS.log and DISM.log, then run DISM /Online /Cleanup-Image /RestoreHealth. If DISM cannot find the repair files, provide matching Windows Server 2019 installation media as a /Source and use /LimitAccess. After the component store is repaired, reboot and retry Windows Update.

Install the latest applicable servicing stack update, or the required servicing stack updates in sequence, before attempting the current cumulative update. A server that has missed several years of servicing-stack changes may not be able to process the newest rollup directly. Download the packages manually from the Microsoft Update Catalog, verify that they match the server edition, architecture, and build, install them one at a time, reboot when requested, and then try the cumulative update again.