WSUS on Server 2022 will not download Windows 11 CUs

I too feel this is UUP related. I doubt this is the reason, because theoretically if you have the latest CU installed on the server you shouldn't need this, but I'm posting here just to have you verify you have the mimetypes.

https://www.ajtek.ca/guides/how-to-prepare-for-on-prem-wsus-uup-updates/

I can tell you that it's working for me. Just loaded my test box and synced 2026.03's 25H2 CU (12,869.98MB) successfully.

You may or may not need to tell BITS to use Foreground priority mode.

https://www.ajtek.ca/wsus/wsus-bits-foreground-priority-mode-vs-background-priority-mode/

Hello.

I would guess that it is likely caused by the Unified Update Platform payloads. To solve this, on your WSUS server, open IIS Manager, navigate to the WSUS Administration site, and increase the maxAllowedContentLength in Request Filtering to at least 20GB so the file isn't being rejected by the web server.

If the transfer is stuck in a transient error state, stop the BITS service and purge the metadata cache located at C:\ProgramData\Microsoft\Network\Downloader\ before restarting the service to clear the queue. Also ensure your IIS server is configured to handle .msu and .psf files by adding them to the MIME Types section if they are missing. Lastly, run wsusutil.exe reset from the C:\Program Files\Update Services\Tools directory to force WSUS to re-examine the file system and resume the download for the missing files.

If you find my answer useful, please mark it as the "Accepted Answer" so other members can find the solution easily. Your help in supporting the community is much appreciated!
Best regards,
Scott Nguyen