Asking for help on Radxa discord i got the answer to check for the FPC ("Flexible Printed Circuit") cable pin orientation and run lspci next.
Turns out it was the cable all along, lspci returned:
# lspci
00:00.0 PCI bridge: Rockchip Electronics Co., Ltd Device 3576 (rev 01)
01:00.0 SATA controller: ASMedia Technology Inc. ASM1062 Serial ATA Controller (rev 02)
and lsblk shows:
# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
sda 8:0 0 4.5T 0 disk
└─sda1 8:1 0 4.5T 0 part
sdb 8:16 0 223.6G 0 disk
└─sdb1 8:17 0 223.6G 0 part
mtdblock0 31:0 0 16M 0 disk
mmcblk1 179:0 0 59.5G 0 disk
├─mmcblk1p1 179:1 0 16M 0 part /config
├─mmcblk1p2 179:2 0 300M 0 part /boot/efi
└─mmcblk1p3 179:3 0 59.2G 0 part /
zram0 253:0 0 1.9G 0 disk [SWAP]
So now it works and i can carry on with making my NAS 😇
cest73's post in Radxa Rock 4D and "Waveshare PCIe to 2-CH SATA HAT+" (Pcie/SATA overaly missing) was marked as the answer