How to create exactly the official images with Image Builder?

I have a MikroTik RB750Gr3 and the 19.07.6 release downloaded from here includes LuCI.

However, if I use the Image Builder from the same directory to build the image myself, LuCI (and possibly other packages?) are not included. Why is this and how do I find out what packages are enabled in the pre-built image? I want exactly the same thing as the official release, but with two extra packages (wireguard and luci-app-wireguard) built in.

Also, I read something about OpenWrt supporting reproducible builds, but every time I regenerate the image it has a different SHA-256. Is this supposed to happen?

There is a ".manifest" file in the downloads folder, that contains the list of packages included in the image. You can compare that with the output of "make manifest".