NRF52840 Sense - CircuitPython REPL in mu editor not opening

I am trying to program the Seeed NRD52840 Sense in CircuitPython with the Mu editor as mentioned in the wiki page.

The code seems to work correctly (led is blinking) but I am not able to open the REPL/Serial terminal.

I tried to load both frimeware : the on the wiki page and the one on This does not make any difference.

Many thanks for any feedback.