Thank you for your comment.

I installed thermald on my Lenovo T480 with Debian Bookworm and I get 20% better results in stress-ng. The fans are a bit louder now under high load and off under low load.

Without thermald:

  $ stress-ng --matrix 0 -t 3m --metrics-brief
  stress-ng: info:  [3755113] setting to a 180 second (3 mins, 0.00 secs) run per stressor
  stress-ng: info:  [3755113] dispatching hogs: 8 matrix
  stress-ng: info:  [3755113] stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s
  stress-ng: info:  [3755113]                           (secs)    (secs)    (secs)   (real time) (usr+sys time)
  stress-ng: info:  [3755113] matrix          2278812    180.00   1437.43      0.27     12660.06        1585.04

With thermald:

  $ stress-ng --matrix 0 -t 3m --metrics-brief
  stress-ng: info:  [3755550] setting to a 180 second (3 mins, 0.00 secs) run per stressor
  stress-ng: info:  [3755550] dispatching hogs: 8 matrix
  stress-ng: info:  [3755550] stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s
  stress-ng: info:  [3755550]                           (secs)    (secs)    (secs)   (real time) (usr+sys time)
  stress-ng: info:  [3755550] matrix          2791272    180.00   1404.32      0.57     15507.06        1986.83

I just installed it using apt and did no extra configuration. My system was anyway configured for balanced power mode. Why is thermald not installed on desktop installations by default?