gotsnow80
Adb works with the phone fully functional and with debugging on.
You could try turning off the phone for 5-30 minutes.
For sideloading:
At the bootloader screen, use the volume buttons to cycle through the menu. Push power when you see that it is on recovery.
At the green android on their back, hold power button down, click volume up and let go of volume up, let go of power button.
Instructions
https://grapheneos.org/usage#updates-sideloading
For your pixel 6. (non pro)
Don't unzip these. Only only need 1. If you start with normal and it says the version on your phone is 1 second newer then use security preview .zip
Normal
https://releases.grapheneos.org/oriole-ota_update-2026071500.zip
Security preview
https://releases.grapheneos.org/oriole-ota_update-2026071501.zip
What boot slot you're on doesn't matter. There is only 1 full copy of the OS on your phone currently. Boot slot A won't work at all.