I've created a good many new clients and jobs over the years without issue.  Somehow the last one I created seems to have defaulted to "email" for the invoicing.  I have tried changing to both the 'Mail' and 'None', exiting the program and coming back in each time, but to no avail.  I just upgraded to the 2021 version this week, so I'm not sure if that has anything to do with this, but it's VERY frustrating.  I, too, had to resort to letting it email the invoice to myself just so that I could move onto something else.  Just ridiculous.