After many investigations, tests, etc. I have a solution (kind of...).
I read that in some cases, slow USB devices don't answer enough fast to the host and are not recognized. In my case (this is important, you'll see later) is a SATA SSD disk with a USB-SATA adapter.
The solution for this is to change the kernel paramenter usb_storage.use_delay from 1 to 5.
The only method to change it that worked for me is (I'm sure there must be a better one) create a custom image and before starting to compile (but after setting the other parameters y the GUI) , edit ~/armbian/cache/sources/linux-mainline/linux-5.8.y/drivers/usb/storage/usb.c
and change the line:
static unsigned int delay_use = 1;
to:
static unsigned int delay_use = 5;
No other method worked, neither adding a file /etc/modprobe.d/custom.conf with "usb_storage.use_delay=5", neither configuring armbianEnv.txt with:
root@nanopineo3:/boot# cat armbianEnv.txt
verbosity=1
bootlogo=false
overlay_prefix=rockchip
fdtfile=rockchip/rk3328-nanopi-r2-rev00.dtb
rootdev=UUID=7ea7a792-8bff-4c9a-be74-934d4ebfcce0
rootfstype=ext4
console=serial
usbstoragequirks=0x2537:0x1066:u,0x2537:0x1068:u
extraargs="usb_storage.use_delay=5"
BUT (and this is a very important BUT), with this parameter I was able to made it work with one specifica USB-SATA adapter, a external cable with USB in one side and SATA in the other (https://es.aliexpress.com/item/33024624761.html?spm=a2g0s.9042311.0.0.274263c0wxlBDr), but with other adapters i.e. external SATA to USB boxes it doesn't. They're recognized by lsusb:
/: Bus 05.Port 1: Dev 1, Class=root_hub, Driver=xhci-hcd/1p, 5000MB|__ Port 1: Dev 6, If 0, Class=Mass Storage, Driver=uas, 5000M
But don't appear as a block device (no /dev/sda)
I'm investigating this last issue.