SDCard ignored for booting

[boeker]

I have bought two new pinephones beta edition with 3 GB RAM and 32 GB EMMC / Community Edition in october 2021 .
Neither one seems to recognize the SDCard nor do they boot from that SDCard as they should according to documentation, not with JumpDrive or the multiboot image nor with the Mobian image, they just ignore the SDCard.
Using the USB-C drive the SDCards with adapter are recognized but the system won't boot from that drive.
I have created the bootable 16GB SCCards (here mmcblk0p1) on Debian using dd:

[boeker@plasma-mobile ~]$ dmesg|grep mmcblk
[    1.357949] mmcblk0: mmc0:e624 SC16G 14.8 GiB
[    1.361013]  mmcblk0: p1
[    1.455482] mmcblk2: mmc2:0001 ASTCXX 29.0 GiB
[    1.455845] mmcblk2boot0: mmc2:0001 ASTCXX partition 1 4.00 MiB
[    1.456187] mmcblk2boot1: mmc2:0001 ASTCXX partition 2 4.00 MiB
[    1.458338]  mmcblk2: p1 p2
[    2.421494] EXT4-fs (mmcblk2p2): mounted filesystem with ordered data mode. Opts: (null). Quota mode: none.
[    4.123982] EXT4-fs (mmcblk2p2): re-mounted. Opts: (null). Quota mode: none.
[    5.400016] FAT-fs (mmcblk2p1): Volume was not properly unmounted. Some data may be corrupt. Please run fsck.