CPU FAN maintains its lowest ~632 rpm even if PWM is set to 0. So it is not possible to stop CPU FAN. Max noticed RPM: 4300

Very loud bottom fan, 2 pin only, connected to 4pin connector on MB.

• Everflow Model: R1292215BL
• 92 x 92 x 16 [mm]
• 12V / 0.20A
• Replacement Noctua NF-A9x14 PWM
  • 12V / 1.32W / 0.11A
  • 92 x 92 x 14 [mm]
  • 19,9 dBa
  • 50.5 CFM
  • 2200 rpm

PWM control is not working. BIOS/MB design is broken ? Workaround is to use CPU FAN PWM to control also bottom FAN.

AMD Ryzen 7 5825U max temp is 95

Default BIOS for FANs PWM:

• CPU Fan: Enabled
  • Fan Off(0x68) 30
  • Fan Start(0x69) 35
  • TFull Speed(0x6A) 92
  • Start PWM(0x6B) 40
  • Automatic Mode Control (0x6C) 2
  • Delta Temperature(0x6D) 1
• System Fan & System Fan 2
  • Fan Off(0x70) 20
  • Fan Start(0x71) 25
  • TFull Speed(0x72) 80
  • Start PWM(0x73) 130
  • Automatic Mode Control (0x74) 4
  • Delta Temperature(0x75) 1

Description:

• Fan OFF: At this temperature the fan remains off.
• Fan Start: At this temperature the fan starts to rotate.
• Full Speed: Not related to PWM. Over this temperature the fan will spin at full speed.
• Start PWM: This is the percentage of speed at which you want your fan to start spinning when it reaches the temperature indicated in “Fan Start”.
• Automatic Mode Control: It is PWM slope on 1/8th steps. Setting of 8 in BIOS gives value of 64 in ITE8613e chip register (and also linux sysfs). Max in linux sysfs is 127.
• Delta temperature: default is 2

How to setup CPU fan. To keep fans quiet and not rotating when possible:

• Full speed = 89. To protect CPU. Max CPU working temp is 95. Consider that spin-up of CPU FAN takes time. Mine is 89 so if CPU reach 90 it goes full speed.
• Start PWM = to 25 (percent). This is because 2nd chasis FAN connected to CPU fan start rotating from this value.
• Fan OFF = 50
• Fan Start = 60
• Automatic Mode Control = 4 (raw value 32)