Thank you Bill for the link how to set up the audio.
I am aware of adjusting the audio mixer in Windows. This worked fine with my FT1000 and FTdx1200 where I set the mixer to a zero ALC reading at the TRX meter.

But, this does not work for the FTDX101. I believe that this TRX has a kind of ALC in the audio circuit (I had also problems in setting up the mike gain and processor at first). The audio in the transmitter  SDR of the FTDX101 works different as you would expect.

Anyway, when I set the audio mixer slider in Windows to -35 dB (!) the PWR slider in WSJT works properly. At max, I can get the maximum power as set in the TRX o/p setting and slide it down to zero o/p.
Any setting > -35dB of the audio slider causing a behaviour that what ever you set with the PWR slider, the output power increases automatically to the maximum setting (except for when you slide it complete down to the bottom).

So maybe this has something to do with the FTDZ101 (settings?)

73, Nic PA3ADU