OK so how can I help to fix this issue?

fdisk -l Disk /dev/ram0: 4 MiB, 4194304 bytes, 8192 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk /dev/ram1: 4 MiB, 4194304 bytes, 8192 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk /dev/ram2: 4 MiB, 4194304 bytes, 8192 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk /dev/ram3: 4 MiB, 4194304 bytes, 8192 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk /dev/mmcblk0: 14.84 GiB, 15931539456 bytes, 31116288 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0x4c58faaa Device Boot Start End Sectors Size Id Type /dev/mmcblk0p1 8192 30801920 30793729 14.7G 83 Linux Disk /dev/zram0: 483.1 MiB, 506564608 bytes, 123673 sectors Units: sectors of 1 * 4096 = 4096 bytes Sector size (logical/physical): 4096 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk /dev/zram1: 50 MiB, 52428800 bytes, 12800 sectors Units: sectors of 1 * 4096 = 4096 bytes Sector size (logical/physical): 4096 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Out of desperation, I plugged in an SSD via USB adapter, and it is recognized as: /dev/sda: Detected One might think the SATA connection is defective, but when I boot with the Ubuntu 16.04 image without changing anything, the SATA SSD is recognized! So the SATA connection on the BPI M1+ works, and so does the SSD. It's definitely the Armbian image that's the problem, but where exactly is it?

Userspace has nothing to do with hardware features. I don't know what is the case for A20, but for many others, OTG functionality is driven with overlays. If there are no overlays, you need to edit device tree and change its role. If that doesn't help, it is more complex problem. More complex, perhaps days / weeks to debug and fix. Most of (Armbian) kernel developers are long gone from this 10+ years old platform and users can't help. Also look into previous builds. Finding out when this broke is half of the solution https://fi.mirror.armbian.de/oldarchive/ or by finding a kernel that works https://docs.armbian.com/User-Guide_Armbian-Config/System/#alternative-kernels With any userspace (trixie/noble/jammy ...) Probably all A10 and A20 boards share this problem.

BPI M1+ tested with: Armbian_23.8.1_Bananapim1plus_jammy Armbian_24.11.1_Bananapi_noble Armbian_26.2.0-trunk.342_Bananapi_noble and the SATA interface doesn't work on any of the three. Does nobody use a BPI M1+ with an Armbian image where the SATA interface works?

For your information, I have a BPI M1 BPI M1+ BPI M3 All three are currently running Ubuntu 16.04, where SATA works, but it's a very old version. All tests with Armbian were performed using the BPI M1+, although SATA did not work.