You are welcome, glad to help if I can! Our setups are a bit different. I'm on BIOS F20 and use HDMI + DVI with an RX 560. Here are some things I would check:
1) Make sure your kexts are up to date. Assuming you are also on Catalina (see post 285 for the rest of my latest upgrade details).
- Lilu.kext 1.3.8
- Whatevergreen 1.3.3
- AppleALC.kext 1.4.2
2) Set ErP = Enabled (BIOS) - really controls shutdown state and power allowed, but worth a try perhaps.
3) Stop/Remove any apps or other back-end services that could potentially be playing a role in the wakeup? (at least to troubleshoot)
Note: the Activity Monitor system app has a column you can show called "Preventing Sleep", perhaps this could be useful to determine involved processes. I recall using some PM commands in the past that may also help with determining this type of problem. I even had Chrome preventing sleep at one point..
I was going to say look into Darkwake settings, but I am not sure this is even a thing any more. I used to use this setting in past versions of the OS to help with taming wake from sleep issues.