Hi Paul,
So it seems you are fully up to date.
This is a list of the issues tagged emarald at Gitlab. Personal opinion (no experience of the device) one might say that this has been something of a difficult situation for a while, as not all users seem to report exactly the same thing.
Maybe this VoWiFi not working on Teracube Emerald – #5417 is close to your situation? However there are similar issues; https://gitlab.e.foundation/e/backlog/-/issues/6391 and https://gitlab.e.foundation/e/backlog/-/issues/7217. It might be a good idea to try to fine tune your observations to add to the most suitable link.
To add to an issue please read Report an isssue
Alternatively, as a Murena purchased phone you might consider the “Contact us” Support form: https://murena.com/contact-us/.
The form is mentioned in Week 45, Development and Testing Updates under a sub-heading at the foot of the page. /e/OS website and social media Links and Support.