How to debug. VScode Mbed

I try to debug a simple program. I have a value test and the onboard LED.
I try to “watch” both values. But i can not add them under the tab ‘watch’.

I installed VScode added and started a project with mbed as framework.
I run the code on a Nucleo F401RE.

How can I add value to the watch window so they are monitored all the time.

i found the problem with the variable test. but how can i watch the state of the led?