I found the solution to disabling this RemoteFXvGPUDisablement.exe running at startup. Simply disabling the task schedular termsrv->RemoteFX.
Is there any way to update Windows 10 but avoid feature update?-disableremotefxvgpu.jpg
No idea though how this task scheduler is there on this build of 1903 as it wasn't before.

But I can verify that so far no forced Windows updates since setting Target to 1903! I got offered the update for Edge Chromium, which I'm not really interested to install as I have fears that I can't disable the auto update on that. But the option is there to manually click the Download button. It is not forcing to download it, which is good news.

Seems like indeed, the version I've got is the final build as verified here. Windows 10 version 1903 - Wikipedia

"The update reached end of service after the release of build 18362.1256 on December 8, 2020"

This matches my build version 18362.1256. As the old version that I had before 2 years ago was 18362.720. It seems only the security updates are missing, but I don't think that's a big loss. I simply manually downloaded the security update from catalog to remove the Adobe Flash Player.

Specify_target_Feature_Update_version_to_1903 is the only real way to stop Windows 10 from auto installing newer versions of Windows 10. Without this option, you really are stuck.

I added this registry with the LAN cable unplugged when I installed Windows 10. After that re-plugging the cable meant Windows is only searching for 1903 updates.

It's a real pain because in future if we ever want to install and remain at a specific version of Windows 10 we have to go through this procedure again.