On the CC6UL system-on-module
UART1 is connected to the Bluetooth chip (on modules with Bluetooth).
All other seven UARTs are available for peripheral use.
However:
On the ConnectCore 6UL SBC Express:
UART4 is available on the expansion connector (2-wires, TTL level).
UART5 is routed to the console connector.
I do not believe UART2 is available on castellated pins that SBC express is using on this SOM.
You can doublecheck this using DIGI CONNECTCORE SMART IOMUX tool: