I'm using version 60.6.1 on Windows 10 OS. Just checked using same process as you mention. After answering yes to two questions a window opens so I can choose a folder and both pdf docs are created. So this is working.

What OS are you using? what version of Thunderbird?

Test in Safe Mode: https://support.mozilla.org/en-US/kb/safe-mode-thunderbird

Do you get same issue?

If yes, please restart computer in 'Safe Mode with networking' Then start Thunderbird as normal. Do you get same issue?

Hi, I'm also using Windows 10 64bit with Thunderbird 60.6.1. However, restarting it in safe mode there are fewer options in the first menu, and "Save selected messages" isn't one of them, so I can get no further with the test.

In the meantime, in normal mode, I ticked the two "don't ask me again" boxes on the subsequent questions and as soon as I click on "PDF" in the second options menu, both menus disappear and nothing else happens.

What version of 'ImportExportTools' are you using? I'm using 3.3.2

Nailed it! I had V3.3.0 which claimed not to have any update available, but I re-installed it and it then showed V3.3.2 which works. Thanks for all your help.

Switched it to automatic update from "Default"