DMC

As far as I remember mostly works, with single ethernet, why not create new build with 6.15 and right dt file for 3B?

Sure if You don't mind my PCIE debug stuff and some memory patches, let me put image somewhere and we will see if it's ok, I literally tested only nvme, double ethernet and pcie slots. ok, done: https://www.swisstransfer.com/d/eb79c889-1225-49a6-a674-947124fa7b79 let me know if it uploaded correctly and work?

Have You compared pcie sata adapter vs native sata vs nvme speeds? All in A+E slot (pcie 2.1 x1) Any real advantages for native sata?

I also could not run it, checked different sata cables, different ssds. I tested that on 3A, 5A and to my suprise same setup worked on 5B (on vendor 6.1 and edge), so it's not the matter of damaged cable or component. Obvious solution is to use any pcie - sata adapter like m.2 A+E with JMB582 (dual sata) or m.2 M ASM1166 or JMB585, I got it on one Rock 3A paired with radxa penta sata kit (works great with additional 2.5G pcie adapter).

Have You managed to get it running? I was able to get it to work on my board, but it drops sata link constantly already checked different ssd, cable, power source (PoE vs usb-c), few kernels and still can't get stable sata link. I did not checked nvme with sata overlays, I assume it's problematic with sata on Your side?

What kind of image do You need? desktop or cli? As far as I remember I built few images for 3B with both ethernet ports (plus one extra with 2.5G A+E adapter)