I'm back. After a few months, I decided to give it a go again and install a fresh Catalina 10.15.4 on another Dell 3670 desktop PC using the latest Unibeast and Multibeast. Install went well and everything is working, except, of course, audio.
Extracted a virgin AppleHDA.kext from a later Mojave installer, and tried the steps listed at the beginning of this thread. No joy. AppleHDA is not loaded.
System Report/Extensions does show both AppleHDA's (Catalina and Mojave) but both show "No" for loaded.
Tried manually loading the Mojave version of AppleHDA using kextload, and it DOES load! No errors, and System Report/Extensions shows it is loaded! So why won't it load at startup? BUT, even though it loads manually, there are still no audio devices.
So I don't get it. I cannot figure out why AppleHDA (either Catalina or Mojave versions) won't start during boot.
Oh, and I did try Clover's ForceKextToLoad feature and listed "\Library\Extensions\AppleHDA.kext" and that did not force it to load either.
On another Dell 3670 I have Mojave running perfectly with audio. Hackintool lists ALC867 with layout id 13. Same as I am using in Catalina (in Clover, I have inject 13 for audio).
What am I missing or doing wrong?