Ok when you want logs then you get logs, I made you one with H265 and one with AV1 and also I added photos.
The Disk was the same, and now a real banger I tryed a DVD what usualy was encoding with the RTX 3060 with around 590 frames, with the 5080 same fast like a BluRay around 100 frames.
I added you the sensor screnshoot too of the GPU, like you see the card is baryl used, it is basicly in sleep mode.
And because you log not say it here is my Rig info
Motherbord: MSI MPG X870E Carbon
CPU: AMD Ryzen 7 9800X3D
RAM: 64 GB DDR5-5600
GPU: MSI GeForce RTX 5080
So it is not my PC, there is a problem with DVDfab and UniFab using the 5000series.
About the UniFab problem I have make a seperate post in the UniFab forum, because the AI is not working. Maybe you could do something about it too.