Ref - same issue link
Everything enabled but still facing cart expiry in hour issue for guest checkout, any idea? My Magento version is 2.3.1
"If a guest shopper later logs in or creates a new account, the shopping cart is restored." (from the Magento documentation, link below).
Therefore you will lose the cart information when the session expires but will see the data again if you create an account or login.
You can also just increase the session lifetime to a higher value (default is one hour). Depending on the traffic you have, the session handling / system ressources and the expectation of how long the cart should be available you can use here a value that could be an option for you.