Thanks for the response Michael but I've been doing all that. Some more screens from testing today. I'm using Chrome but it didn't work for this tenant in Edge or Firefox either. It's the default enviroment for Flow. Anything to do with the number of connections created? I can delete this 'send email' stage and add a new one but it's the same issue.
I also cannot delete or rename the steps with the 'send an email'.
This client has MFA security. But I don't have the email issue in my private tenant. So is there a permissions issue?

