I see about a month ago you stated that you purchased an “unlocked” Nexus 6p. To reiterate what @beng is saying, if you’re stating that the bootloader is unlocked, then your 6p will no longer receive over the air updates (OTAs). Meaning, “checking for updates” will yield no results.
I’m not certain it would work but you could try enrolling in the Android Beta Program to see if that will push OTAs to your 6p. Outside of that you’d have to manually install updates yourself.
You may find the following link helpful:
If your bootloader is not unlocked and you’re still unable to pull OTA updates, I would recommend opening a support ticket.
Have a great weekend!