On microcontrollers there are analog outputs which output a pulse width modulation digital signal.
I can set the output to whatever I want as long as it's not greater than 5 V.
For example, I want set the output to 4 V because there's a module that needs a 4 V power source. Can that module run without problems if the power source comes from analog output PWM?
PWM outputs aren't analog; they are digital, switched with a certain duty cycle.
The idea that they are analog probably stems from the unfortunately named analogWrite() function as implemented on Arduinos, that sets a duty cycle on a PWM pin.
It is a misnomer; an 80% PWM signal on a 5 V MCU is 5 V for 80% of the time, and 0 V for 20% of the time; it is not 4 V, it is only 4 V on average.
Loads that have a maximum supply voltage of, say, 4 V shouldn't, in general, be driven with a 5 V signal, PWM or not.
Also, a PWM signal from an MCU can only source a very small current (5 mA to 20 mA for MCUs used on Arduinos), and can't be used to power loads larger than, say, a small LED.
It can be used for PWM-switching an external power source for a larger load, though, if that load can work with PWM and the voltage stays within its specifications, as above.
There are limited applications where you can use a PWM signal as a power supply: if the current requirement is within what an IO pin can supply (a few milliamperes) and if the load (a) is ok with a PWM supply, something like a small light bulb, or (b) the supply is smoothed with an LC filter (inductor and capacitor). If you’re thinking of driving an LED you’d probably find that PWM will work although it’s not ideal, the IO pin will likely current-limit during its ‘on’ phase at a level that won’t damage the LED but it’s not an elegant solution.
