Actually leather could.
Prop 65 contains over 900 chemicals.
From an article I was reading: "For example, products made of vinyl (purses, belts, zippers), leather or imitation leather (shoes, jackets), or brass (door knobs, key-chains, frames) may contain lead."
If anyone is interested here's a current (though it can change) list of chemicals covered under Prop 65:
https://oehha.ca.gov/proposition-65/chemicals
Please note that products that contain chemicals but in a level low enough they are exempt from Prop 65 warning requirements. Those are called Safe harbor levels.
https://oehha.ca.gov/media/downloads/proposition-65/general-info/safeharborlist100418.pdf
Also note stricter requirements were enacted for products manufactured AFTER August 30th, 2018 so there are possibilities of getting items manufactured before that date that are not subject to the stricter rules.