I'm trying to revert a Pixel 6 back to stock.

OEM unlocking is enabled but the device state will not change to unlocked. I've tried restarting with and without OEM unlocking enabled, re-enabling, etc.

Please tell me what I'm doing wrong so I can erase the boot key!

How are you trying to reflash the stock image? Web installer from Google? In that case it should trigger the unlocking of the bootloader by starting the process. If you have adb/fastboot installed, you can trigger the unlocking manually by typing
fastboot flashing unlock
in the terminal on your computer while your Pixel is on the bootloader screen.

OEM unlocking does not unlock the bootloader, it allows the bootloader to be unlocked. So head back into fastboot, hit the unlock bootloader button, confirm that action on your phone, then you can remove the key and finally use Google's web installer.

Using the Graphene installer first to forget the boot key.

It worked to use the fastboot unlock command. Thank you both!

Can you describe your process in detail? From your initial post, it seems like You are enabling /disabling OEM unlock & expecting that to change the LOCKED state seen in Fastboot BL menu (Vol. ↓ + PWR).
OEM unlock just allows you to then proceed TO the process of unlocking the bootloader.

If This is incorrect,
from what device state indicator is your anticipatory expectation linking stimulus derived? Please provide this and a detailed list of your process.