Could not delete so just edited this to say nothing.
Yes...You are missing something
The Microsoft Enablement Packages will not Upgrade Windows. In fact, they contain 0 lines of code. They do nothing more than updating a few registry keys.
Windows 1903 and 1909 are 100% Binary Identical.
Windows 20H1 (2004), 20H2 (2009), and 21H1 (Also 2009) are all 100% Binary Identical.
The enablement package will simply "Unlock" features that are hidden inside cumulative updates. The is why they are called 'Feature' updates versus upgrades.
Going from 1903 or 1909 to Windows 20H1/20H2/21H1 will require an upgrade.
Basically, you will want to create a bundle to perform the upgrade. There is a ZPM cool solution about how to make the bundle and convert it to a patch, but I would not recommend making it a patch. The Cool Solution is a good starting point.
If you have a single site, then one can use the article closer to AS IS and reference a UNC Share.
If you have multiple sites, then most likely you will need to use the Content-Repo. There are some tips and tricks I can give you to make the bundle much more efficient. Content bundles tend to get really slow when you the content is in the many GBs, but it is easy enough to workaround.
It can be found here...