How to tune PWM fans for CPU and Case in Ubuntu 20?

AFAIK fan PWM is not enabled, you control the fans through I2C. See Fan control and Fan PWM status?. In my case once I switched to ACPI+edk2 the fan quieted down instead of running full throttle all the time. Not sure how much control you are looking for but you can probably use e.g. cpufreq governors.