Food grade silicone would be my choice. Also potentially a non-stick spray like Pam could work and will not poison you. I would avoid motor oil or PTFE as when it does reach flash point the off gas is toxic.
Here is a complete how-to by some unknown dude.
https://greenwaykitchen.com/how-to-lubricate-convection-oven-fan-2/#google_vignette