Hi,
I have the same problem as patoberli, different board but esp8266 based.
The 2.7.4 core doesn't allow to select any esp 8266 board until upgrading the core to 3.0.2.
After that I can choose the board and still work even downgrading core to 2.7.4 .
Closing the Ide and reopening=same issue again...
Hope it helps
I forgot: Ide is 2.0B9 , did not try B10 yet
Davide