This happened to me amongst my testing, mainly on 0704 BIOS.
In my case it wouldn't recover (wake up) at all. Had to hard reset it (power off and on), then I'd have a red flashing light (every 4 seconds) which meant no Boot Drive Discovered. To recover the system I had to CMOS reset it by bridging the two pins and then re-configure bios again.
Can't say I narrowed it down as at the time I was heavily focused on TB2 testing, trying to get my UAD Apollo MKII to connect with the TB2->TB3 Apple adapter (with no luck) and thought the Thunderbolt was causing that sleep issue. XMP on/off, using speeds 4800, 5000 and 5600, still happened.
So I updated to BIOS 0814 tested again, no TB2 connection, but in the same instance I borrowed a friend's UAD Apollo Twin X (TB3) to test, and that worked no problem, hot plugged, on/off while in the OS, cold boot, warm boot, everything works. So I went and bought one, and, since then, I haven't experienced that sleep issue.
Now was it the Thunderbolt? Was it the BIOS version? Can't say..
Side note:
I'm on Big Sur 11.7.2
OC 0.8.8
Latest kexts/drivers (at the time of this post)
Thunderbolt driver 1.41.1340.0 (NVM 38.0)
SMBIOS MacPro7,1 & iMacPro 1,1 tested.
What I can say is, I downloaded your EFI to compare to mine quickly, I noticed you're using different **z790.aml files, are they just renamed from Casey's z690 ProArt EFI? Or they different? I'm using his z690 ProArt EFI, updated it to all latest kexts/drivers, added BRG0.aml as I'm using the 6900XTXH variant, fresh installed Big Sur, and it worked. Perhaps use his and test (if not already).
Few questions..
What BIOS version are you running, 0704 or 0814?
Do you have any thunderbolt devices connected? Try cold booting without them connected and put it to sleep to see if it does it again.
Try using SSDT-MAPLE-RIDGE-RP05-V1B.aml instead of V2, I'm currently running V1B and haven't had issues.
One more thing that may not be relevant, but good to test.. What monitor are you using? How is it connected to your GPU, HDMI or DP? In Displays, do you have the resolution SCALED or normal?
I discovered in my case, whenever i had the Display SCALED, i noticed my VRAM would increase to the point of no return (iStatistica showed it) and the machine became noticeably slower, even re-scaling the FINDER window would eat the VRAM...?!
When the Display is set to "Default for Resolution" there is no problems whatsoever, and i tested this by opening Logic Pro X with 20+ graphical meter plugins, 10 youtube videos in google chrome, plus Netflix and Prime in Safari with no VRAM issues.
If you've scaled it, Try Default For Resolution and put it to sleep to see if the same problem occurs.
Hopefully there's some info here that can help you, let us know how you go!