Thank you so very much!

I got the best results with: fan tacho out - pullup resistor 10k to 3.3V - series resistor 3.3k - capacitor 100 pF to gnd - esp32 input pin It works successfully with a noctua fan (max 1500 rpm) and a cpu fan (max 2400 rpm). Jelly32 - Do you have a drawing of this? Even a quick sketch. I'm happened...