I applied my TCXO mod above and it seems it works!
I removed the R11 short and soldered in a 10k smd resistor at the pads of the not populated trimp pot.
The 10k resistor is easily accessible now as it sits on "top side" of the DDS pcb when mounted in.
I also covered the TCXO and the pcb from the opposite side with 3mm piece of foam (against the "banana effect").
The measurement is as follows now:
HEX FREQ 2LO
I get the exact 2LO frequency of 124.032.000 Hz with E6 hex.
While measuring at the dummy load (with TX RTTY method) I get my 21.200.000 with 89% set in OTH menu #51.