I had the same issue. Touchpad not working ASUS Zenbook laptop Q409 Series. I2C not working. Started about a month ago. Was not showing touchpad on ANY settings in Windows 11 or MyASUS.
Looked up every possible "solution" online today 7/1/2025....could not find any thing that worked.
After much fooling around myself....THIS METHOD WORKED FOR ME.....
I first deleted/removed I2C device in device manager. It had a yellow caution icon on it.
Then removed MyASUS App.
Next, went to ASUS support website. Drivers and Bios & Firmware. Enter your model # and expand all. I went through and manually downloaded the latest versions of all except for Display, Wi-Fi, Bluetooth and Intel related downloads ( Intel Driver and Support Assistant should have updated these ).
You will have to restart your PC numerous times !! I didn't use the auto-update link ( near top of page in blue print because I didn't want it to download things I didn't need. So, I don't know if that method will work.
Last, I re-installed MyASUS app. Make sure you have your password handy.
My specs....
Edition Windows 11 Home
Version 24H2
Installed on 10/3/2024
OS build 26100.4484
Experience Windows Feature Experience Pack 1000.26100.128.0