On recent kernels when using a laptop with hybrid graphics but not running with the discrete GPU graphics enabled, a regression meant the dGPU never got powered off… Fortunately, for Linux 5.5 — and potentially to be back-ported after that — is a change to restore that power-savings…

Source: Phoronix – Linux 5.5 To Restore Power-Savings For Hybrid Laptops When Not Using The dGPU