I just bought a 2012 Honda civic and the key fob works for everything except using the physical key to unlock the drivers side door. It can start the car though. I was thinking it was the actual lock mechanism?

The fob unlocks all doors except the driver's door? I would guess the door lock actuator is bad.

Key cylinder might be seized from lack of use

Ill try lubricating the lock and go from there. Any recommendations for a certain lube brand?

Brand doesn't matter, either graphite lube, or some something like fluid film

So I used some graphite based lube and a tiny bit of wd40. Barely enough IMO but I assumed it wasnt good for locks. Its still stuck and my key cant turn it at all. So, worse case I have to buy a new key cylinder? Or is there something else I could try? I let it sit and tried turning the key for a bit to move the graphite but it still hasnt budged.

bump

my front driver side door lock also does not work. The will not turn, tried lubricants.

Only option to replace the cylinder and have two keys? One to open, one to start?

That's the cheapest way to do it, can also retumble the new door lock to match the ignition