Device Manager is not straightforward.

The thing is, a Pixel is a whole-ass computer itself, so it's going to have numerous drivers in numerous places.

I have drivers for my Pixel hidden away in places like:

Bluetooth

Sound, video, and game controllers

System Devices

The only stuff I normally have in Portable Devices is ejectable USB hard drives and USB thumbsticks.

The Pixel will only show under Portable Devices if USB file transfer is turned on because then the PC recognizes the Pixel as a removable hard drive/mass storage device.

Under "USB Preferences" on your Pixel, once you plug into your PC, ensure you have enabled "Use USB for: File Transfer / Android Auto" and it should show up in Portable Devices.

If you've done that and it still doesn't show up, you might need to check that the driver for the Pixel got properly installed, and also check your USB cable to make sure it isn't damaged.

Congrats on joining the GrapheneOS enjoyers

Do you have the Google USB driver installed?

https://developer.android.com/studio/run/win-usb

I'd ask in Graphene's Matrix room, they're real helpful over there.

Short of that try a different cable (that was why mine wouldn't work) and it wouldn't let me use firefox I had to use a Bromite (RIP).