Hi Peter. THIS ISSUE IS NOT FIXED, but I have found a potential workaround for you if you have access to a mobile phone not associated with your Microsoft account.
I've managed to set up a separate, new Microsoft account on my partner's phone, using only the phone number instead of an email address as the login details. Once I'd done this, I was able to log out of my Microsoft account on my computer and log in on this new account to have a normal meeting - the phone number being the User ID in this instance, instead of my email address.
We're still not able to use Teams on any device under our existing Microsoft accounts, so this is just a workaround for your urgent meeting - NOT a resolution to the problem at all.