Hi, I’m happy to announce that VoLTE and VoWiFi have started working for me recently in Czech republic with Vodafone CZ. The only little problem is that nobody knows why and support pages of FP and VF indicate otherwise 
If you want details, read on 
I had a long-standing support request trying to figure out what needs to be done. FP told me Vodafone has to contact them to sign a contract. Vodafone told me FP has to reach out to them. The classical never-ending story.
Then I figured out Wifi calling started working, although in a kind of hidden mode. All configs were greyed out, but when I switched to airplane mode and turned on Wifi, it worked.
And then, some time in June 2023, both VoLTE and VoWiFi finally started working properly! Yay!
So I checked the support page of FP: https://support.fairphone.com/hc/en-us/articles/9779766652689-VoLTE-VoWi-Fi . Vodafone CZ is not listed. I also checked the Vodafone CZ support page: https://www.vodafone.cz/_sys_/FileStorage/download/3/2082/ims-sluzby.pdf/?nc=21 . Fairphone is not listed. So I opened another support request with FP to add Vodafone to the list. And FP support told me:
In this case, if Vodafone CZ is still not listed this would be an indication that we have not yet confirmed official support for these features with this network operator.
Okay, so… What does this mean? I’m confused, but definitely happy that it works now (and I hope a future updated will not “correct” it).