Hi Piotr,
I apologize for my incorrect information.It is a problem of my theme, which by analyzing the logs has obsolete parts of the Woocommerce code, and with Woocommerce 4.0.0 and your plugin Flexible Shipping, it does not show me the shipping costs on the Cart page. (don’t work both those set with Flexible and the default method of Woocommerce).
With version 3.9.3 I it works properly.
This is why I said my wrong conclusion. I’m sorry
In fact, I asked for an update of the theme.
Thank you