You can safely stop the update advertisement with the next registry change:
On the right pane, double-click the “TargetReleaseVersion” entry to open it. If you don’t see this entry, then in the right pane, right-click anywhere blank and select New > DWORD (32-bit) Value. Then type “TargetReleaseVersion” (without quotes) and press Enter to create the entry.
Double-click the "TargetReleaseVersion" entry.
In the “Edit DWORD (32-bit) Value” box that opens, click the “Value Data” field and enter “1” (without quotes). Then select “OK.”
Edit the "TargetReleaseVersion" entry's value.
Once again, on the right pane, double-click the “TargetReleaseVersionInfo” entry. If you don’t see it, then right-click anywhere blank on the right pane and choose New > String Value. Type “TargetReleaseVersionInfo” (without quotes) and press Enter to make the entry.
Double-click the "TargetReleaseVersionInfo" entry.
Here we’re going to enter the release update that we want to remain on. At the time of writing, the latest Windows 10 release is the 21H2 update. To determine the current version, review the official Microsoft documentation on the latest version of Windows 10.
On the “Edit String” box, click the “Value Data” field and type “21H1” (without quotes), or whatever your preferred release is. Then click “OK.”
There is no reason why reverting from Windows 11 would block you from receiving regular windows updates, unless your system is already fully updated. If you want to doublecheck the Update system, I would recommend:
Reset windows update components: https://answers.microsoft.com/en-us/windows/forum/all/how-toreset-windows-update-components-in-windows/14b86efd-1420-4916-9832-829125b1e8a3
Then Search for Updates, and then read the WindowsUpdate.log to find if there are any discovery issues.
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