I assume you are being asked for a primary password. I never use one, I am the only one with access to my PC and I see no need for local encryption of my stored passwords beyond the default used by Thunderbird. However there are two possible password requests here; There is a primary password, which is a "password encryption" password you set in Thunderbird. I do not use it at all and it is only invoked if you choose to invoke it. That is not to say there is not "security" software out there suggesting folk use it. Then there is the password request that pops up when you click on the show passwords button in the dialog. This is not a Thunderbird password at all, it is the password set on your operating system to access your user account. This is often blank. Does it appear after you click the show passwords button? I have spent a little time trying to sort this out, and I think it has something to do with this bug https://bugzilla.mozilla.org/show_bug.cgi?id=1896287 as it appears to have landed in the V128 time frame, but I am struggling with acces denied messages on the bug system. So can you get back to me if your windows password or a blank one does not work and I will try and get help with the topic.