Hello! I think the reason for only UART0 being enabled is that this is the only one piped to the FPGA by default:

The several "USB-UART" interfaces presented here: https://pico-ice.tinyvision.ai/md_getting_started.html#autotoc_md6
Are not actually connected to UARTs. I should update the doc to avoid confusion and be more correct.

They are instead bound to different features as described.
In hope I understood your question well, feel free to ask again if I missed something!

I understand that they're only virutal uarts.

My question is, if i define ICE_USB_UART1_CDC to 1, what will happen? will it work? do i get 2 uarts to fpga?

if i define ICE_USB_UART1_CDC to 1, what will happen? will it work? do i get 2 uarts to fpga?

As you guessed, you would not, and modifying the firmware would be necessary.

pico-ice-sdk is here to enable to quickly put together a firmware that can be used with the FPGA.
It is aimed to be modified at compile time, i.e. with macros.
It contains examples which acts a bit like reference implementations.

pico-ice-default is here to provide most of the SDK features in a ready-to-use way.
I have not thought at bringing configuration for it before.
Would an example in pico-ice-sdk/examples with dual UART interfaces enabled work for you?
That would avoid adding code that is disabled by default.
Was there other features that you wanted enabled? Such as the USB-serial to SPI interface?

Was there other features that you wanted enabled? Such as the USB-serial to SPI interface?

I've disabled SPI-CDC and enabled UART1