The warning was because of this post: https://forums.mydigitallife.net/threads/windows-10-hotfix-repository.57050/page-569#post-1636024 Implying that the latest .Netfx35-48 CU is not supported with the new .Netfx48 package, then better to just use the older .Netfx48 package and use the latest .Netfx35-48 CU.
Components with same version but different hashes likely explain the errors which I see in CBS.log when trying to install the newer release on top of the previous 2019-12 release, even without any CU for .NET 4.8 installed. There are many good things introduced in Windows 10 and the equivalent server versions but there are few areas which are messy beyond redemption and the update mechanism is one of them.
It is in fact the same with the late 2020-10 Preview Update, promoted to regular update for lack of a better option. I think it is commonly encountered for the .NET CU updates not designated as "Security Update", but "Update" only. EDIT: Sorry, I noticed that I was making reference to the earlier update instead of the later 2020-11. Ignore this post.
At least we now know that the latest .netfx35-48 CU is not working with the latest .netfx48 package but the older .netfx48 package does and then you are on the most uptodate level
As far as I know, there is no official .exe version of the Jan 2020 (signed Dec 2019) release. The official one is still the 26 July 2019 signed release. After applying one of the recent .NET Framework 4.8 Monthly updates, the base version should no longer matter as far as I can tell, other than showing different base versions.
MSFT doesn't seem to follow the patchtuesday scheme for the defender cabs, they update it in the first week of the month, and yes, the original one is not really uptodate (dec. 4. 2020).
MS did release v2 of the cabs in Oct and Nov patch Tuesday cause the platform update wasn't available to be included in the first release. But for some unknown reason, they decided not to update the cabs for this month.
Are the files not already present on a new installed Windows 10 (19041.1) without running the update?