Basicly, you need to use some VoEnabler modelu (don't know if this one is working with latest magisk) and "play" with efs tool till you will success... But I am affraid, that for some carriers is not enought to replace only IMS folder and others folders from extracted mbn should be created/replaced too...
when you mentioned play with EFS? can you share more pointers on that. At least I'll be playing it with some guidance. Thanks.
as mentioned in another thread, my ims_user_agent file contains manufacture, phone model and OS build which could explains why IMS still not registered, because the user agent is still showing unsupported device model for the carrier.