The KB5000736 Enablement Package allows you to go from build 19042 (v20H2) to 19043 (v21H1).
Take action: July 2021 security update available for all supported versions of Windows
The July 2021 security update release, referred to as our “B” release, is now available for Windows 10, version 21H1 and all supported versions of Windows. Release notes associated with these updates might publish with a delay of up to an hour after the updates are available for download. We recommend that you install these updates promptly. For more information on the different types of monthly quality updates, see our Windows 10 update servicing cadence primer.
Source: July 13, 2021—KB5004237 (OS Builds 19041.1110, 19042.1110, and 19043.1110)
Direct download links for KB5004237 MSU file from Microsoft Update Catalog:
Download KB5004237 MSU for Windows 10 v2004, v20H2, and v21H1 32-bit (x86) - 271.3 MB
Download KB5004237 MSU for Windows 10 v2004, v20H2, and v21H1 64-bit (x64) - 587.6 MB
Download KB5004237 MSU for Windows 10 v2004, v20H2, and v21H1 ARM64 - 627.9 MB