I recommend when setting up make menuconfig to build the Klipper firmware to tic the box that says "Enable extra low-level configuration options" and add the pin that is controls your hotend cooling fan to the option "GPIO pins to set at micro-controller startup".
The reason to enable this feature is to prevent jamming your hotend, or melting your toolhead if the controller is reset while your extruder is hot. This can happen after a momentary power outage, or pressing the reset button on your display, for example. After the MCU resets, it will turn on the hotend fan and keep it on until communication with Klipper is reestablished and Klipper has determined that the hotend is cool and the fan no longer needs to be on.
If you have multiple pins that you need or want to enable at startup, separate them with a comma. For example, if you have an SKR Mini E3 V2 (that requires PA14 to be held low at startup) and you have your hotend fan connected to PC7, you would enter "!PA14,PC7". If you also wanted to have your cooling fan that is controlled by PC6, you can enter "!PA14,PC7,PC6". If you want to enable any steppers at startup you can add the enable pins for those steppers as well (stepper enable pins are typically active low so add an exclamation point in front of the pin, just like it's written in your printer.cfg).
The reason to enable this feature is to prevent jamming your hotend, or melting your toolhead if the controller is reset while your extruder is hot. This can happen after a momentary power outage, or pressing the reset button on your display, for example. After the MCU resets, it will turn on the hotend fan and keep it on until communication with Klipper is reestablished and Klipper has determined that the hotend is cool and the fan no longer needs to be on.
If you have multiple pins that you need or want to enable at startup, separate them with a comma. For example, if you have an SKR Mini E3 V2 (that requires PA14 to be held low at startup) and you have your hotend fan connected to PC7, you would enter "!PA14,PC7". If you also wanted to have your cooling fan that is controlled by PC6, you can enter "!PA14,PC7,PC6". If you want to enable any steppers at startup you can add the enable pins for those steppers as well (stepper enable pins are typically active low so add an exclamation point in front of the pin, just like it's written in your printer.cfg).