Moku:Lab waveform generator has fixed 50 Ω load resistors. When you connect the output to a 50 Ω device, the output voltage distributes to the internal load and external load equally. When you connect the output to a high-z device, most of the voltage distributes to the external load.
Changing the 'load' on the user interface does not affect the actual driving voltage. Instead, it only changes the scale for the display. The displayed voltage under the high load is twice the displayed number under the 50 Ω load.