Note: I am using Ubuntu 22.04

I have the exact same model (15ACH6) with the same specs. I searched a lot, and finally found this tool which successfully disabled the Nvidia GPU for me: https://github.com/geminis3/EnvyControl

For it to work, first install the proprietary Nvidia drivers. Then, reboot. Then, run the following 2 commands:

sudo prime-select on-demand 

sudo systemctl disable gpu-manager.service #to prevent gpu-manager from interfering.

Now, clone the repo and run the following command:

sudo python3 envycontrol.py -s integrated

sudo reboot #And then reboot

You will have your Nvidia GPU disabled. You can verify it using this command:

lspci -nn | grep -E 'VGA|Display' #It shouldn't show Nvidia

However, note that, even after disabling Nvidia GPU, my power consumption didn't decrease a lot. From 20W, it came down to about 15W. I measured it using powertop. Let me know how much it reduces for you.