Ok we are getting closer so thank you!
I added the following from the first post you referenced to my build.prop:
#ifdef VENDOR_EDIT
persist.dbg.ims_volte_enable=1
persist.dbg.volte_avail_ovr=1
persist.dbg.vt_avail_ovr=1
persist.dbg.wfc_avail_ovr=1
#endif
Then this allowed the VolTE and WiFi Calling setting to show up and I can activate it but when I try to make a call it still seems to go out over Cellular network and no icon in the status bar to say that it is active etc.
This is the details of my carrier and wifi calling instructions etc.:
https://community.meteor.ie/device-help-187/everything-you-d-like-to-know-about-wifi-calling-218595
I did not try the second post as it seemed to be very specific to a couple of carriers so any other ideas?