First of all congrats on your build! I don't see a lot of these out in the field especially using my dual GPU EFI setup.
With regards to the AMD laptop dGPU, that's a lot harder to explain. Technically it is unsupported and is still experimental. But I did some changes at the time what I thought could make it work, hence ended up with this EFI I've built. But its not perfect as it doesn't work beyond High Sierra.
What you could try on yours first is adding some Whatevergreen boot-args, and see what effect if any you get. The most prominent (for Mojave) would be shikigva=128 or shikigva=40 shiki-id=Mac-7BA5B2D9E42DDD94. One of these two settings could maybe work to enable acceleration on your AMD card.
As you are on the latest version of OC, I think you could also try adding -wegnoigpu as a boot-arg (to disable the Intel). This I believe is a new feature of the latest Whatevergreen >
https://github.com/acidanthera/WhateverGreen
As for the framebuffer settings, yes you could try adding those in too and see if it works. Just remember to backup your current EFI build.