I use this Relay 3Volt double on ESP32, but is not enough, need also a transistor, a diode, 2 resistors and a safety optocoupler
Did you have a link or shall we call it a night?
Sorry, I had a brain fade ( I recently had a stroke). A 3-pin fan only has a tach output.
Only 4-pin fans have a PWM input.
Maybe it easier to dump that 3- pin fan and buy a 4-pin fan.
Leo..
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Unless you can PWM it with a MOSFET. But that's for the datasheet to determine, and OP have yet not given info about the fan. 
Noctua should have PWM control, then the mosfit should also be able to PWM control so I hope it works 
Not all (including Noctua) have a built-in PWM, the 4th pin. So what's left is to PWM by external means, that is, a MOSFET connected in series with the fans power. But you can also kill a fan by applying PWM, not all fans electronic can operate under those conditions.
So now, finally, will you tell us what fan you got? Otherwise it's useless to continue this discussion.
This particular model should be the one with PWM control, then the cable from Nocua that controls PWM where does it connect to the Mosfit board?
A fan with PWM control has a 4-pin connector and four wires.
You don't need a mosfet with a 4-pin fan.
The PWM wire can directly be driven by the Arduino.
All Noctua fans I have are 4-pin.
Leo..
absolutely right, after reading a bit, it seems like I have to have a 3 - 4 pin rpm adapter that came with the fan, but then I can connect the rpm control cable directly to the esp as well?
If the fan has four wires, yes.
Leo..
I don't know why you're so reluctant to share the model number with us, but I've lost interest in this thread now.
What?
Is it 3 or 4 pin??
Do not connect any wires from the fan to the ESP you may damage the ESP
starting to get a pretty good handle on everything now, the only thing is the cable from the fan that controls the pwm, should it be connected directly to the esp? and if so, does it matter which of all you connect to the esp?
Could it be more misunderstandable?
Esp controls PWM, not the fan or the cable. Esp pwm output can be connected directly to Noctua pwm pin.
You can connect other devices to esp32, the fan pwm sink current is very low, almost insignificant.
Above is valid only for genuine 4-pin Noctua fan.
If you have 3-pin fan, it doesn't have built in pwm control input.
ps. sorry if I missed some post here where you tell what exact fan model you have...
See post #33 for the answer