Trying to send mailmerge. After I fillout Mail Merge dialog box and click send, a blank dialog box opens, then I can't do anything (my email draft is frozen), but my mail isn't sent

Trying to send mailmerge. Thunderbird version 147.0.2 (64-bit) I have sent a mailmerge from thunderbird before, so it should work. I have my CSV ready, and I type the email draft. I click the mailmerge icon, and fill out the mail merge dialogue box. After I fill out Mail Merge dialog box and click send, a blank dialog box opens, then I can't do anything (my email draft is frozen)tried sending, and saving, or pressing load (all options highlighted in screenshot). See also screenshot of blank dialogue box and frozen message. I tried closing the blank dialogue box, but the mailmerge is not sent, and after that, I can create a new message, but the mail merge option is greyed out, so I cannot select it. So I shut down Thunderbird and restart, then I can click the mail mergeicon,but same problem,I only get as far as the blank dialogue box. Thank you so much for your help