When a fan supports full stop (0 RPM), the B850M (TUF Gaming) does not return any sensor data, which causes AIDA64 to not show the fan. The fan reappears when the RPM is above 0 RPM. So when configuring the Sensor Panel or OSD, make sure the fans are running. Then add the fan sensor to the Sensor Panel, or select the fan sensor for your OSD. Once configured, you can set the minimum RPM of the fan to 0 RPM and the fan will still show up in the sensor panel or OSD with a reading of 0 RPM.