I've had lots of issues with wifi calling and have eventually discovered there are 2 settings which have to be supported by the operator. Firstly, wifi calling being available. Secondly whether mobile networks or wifi is preferred.
Therefore I have a vodafone SIM which supports wifi calling, with no support for whether mobile networks or wifi is preferred. I also have a second O2 SIM which does have support for the mobile networks or wifi preferred choice.
Since updating to the BETA, the unsupported setting for my Vodafone SIM has become visible. It doesn't work however.
Please see the screenshot. Wifi preferred should only be available on the O2 SIM and is using wifi as requested. Wifi preferred should not be visible for the Vodafone SIM, but it is. Note at the top it is not using wifi calling as requested.