#I created a startup service that slows down the fan on Ubuntu after boot to speed setting 1, and that is inaudible.

[Unit]
Description=RPI-startup Fan Control service
After=multi-user.target
[Service]
User=root
Type=oneshot
ExecStart=/bin/bash -c "echo '1' | tee -a /sys/class/thermal/cooling_device0/cur_state" &
[Install]
WantedBy=multi-user.target

#Copy above content to a file /etc/systemd/system/fan.service.

#And enable it by:

sudo systemctl enable fan.service

#That’s all, no reboot the Pi and Ubuntu will be silent.
#Remember the Raspberry Pi willl automatically throttle when reaching a temperature of 85°. So there is no danger in letting the fan run on speed 1 continuously. Even when your compiling the Linux Kernel.
#Off course you can always check the temperature with, and yes that works also in Ubuntu 23.10 on the Pi

sudo vcgencmd measure_temp

#You can always bump up the speed to 3 by issuing this in the terminal

echo '3' | sudo tee -a /sys/class/thermal/cooling_device0/cur_state