I found the firewall option inside AddClear, sorry, my mistake
But the firewall option does not provide what philbert2k wanted - and what I am expecting too.
I’ve activated Developer mode, enabled mobile data all the time, configured WhatsApp to run on Mobile data only, and it still does not work.
I assume what we need is some sort of tunneling an app connectivity thru a particular network adapter: wifi or mobile, while both must be active and enabled.
Is there a way to do it?