Feature updates from 1803 to 1903 or 1909
Any version older than Windows 1903, has to be updated to the 1903 Feature Upgrade before you can do any other Feature Upgrades. All of the versions of Windows 10 from 1909 onward had their Feature Updates done differently. To speed up the upgrade process, the features were usually already installed in cumulative updates and then were just activated when you chose to update. I came across the same issue when we were updating our systems running older version of Windows 10 using our WSUS server and Group Policy. I had to download the 1903 Upgrade to our WSUS server first and make sure everything upgraded to 1903 and the I deleted the 1903 upgrade and downloaded the 20H2 to the server.
I haven't update our KACE SMA to 11 yet, so I haven't had the chance to use the Feature update tool but I have no doubt that your problem is because the versions are not up to 1903 and can't upgrade to anything above that.
A possible solution would be to put an unpackaged image of Windows 10 1903 on your Fileshare and then running a script through KACE to tell the PC to run the setup file silently. When I did that to update my version of Windows, I used an online KScript, ran it as Local System, selected "Allow run without a logged-in user" and "Run on next connection if offline" I picked Launch a program and put the directory of the install files on my Fileshare, for File it put setup.exe, checked Wait for completion, and for Parameters: /auto upgrade /quiet /compat ignorewarning /noreboot
I /noreboot so, that I could run it during the day and it would finish the install when they shutdown the computer. If you want to run it at night time then you could omit the /noreboot and it will reboot as soon as it needs to during the install.