This problem was seen under Windows 10 and 11 (64) with Thunderbird 128.2.0 and 128.1.1 (64).
I do a right klick on a file and use the function 'send to - e-mail receiver'. A new mail window of tunderbird opens. I start typing the mail-receiver and there are suggestions of known receivers shown. I take one suggestions and klick on 'send'. Nothing happens, it's not possible to send the mail.
Workaround could be: save the mail to drafts, reopen and send it
If I type a new and complete mailadress.
Best Regards, Ralph
