In case any others have the same issue, my WiFi calling stopped working with Vodafone after the last update. I was using Shizuku and Pixel IMS to get it all working.
Anyway, after some research and trial and error if you add an "ims" APN it works again.
Name: ims
APN: ims
APN Type: ims
All the rest were defaults.
Now VoLTE and WiFi calling are working.