Default handler for attachment by type

Ed, thank you so much for your suggestions. I have marked this item as providing the solution, but am posting this additional detail which may indicate that it might be a solution to my use case, but not others precisely. Having a quarter of a century and several gigabytes of history in the wonderful Thunderbird product, I am still cautiously sitting at version 140 and some of the reasons I was getting this failure may derive from that fact. For example, just following your nice instructions to get to Advanced Preferences nearly failed because in this older version the the layout handler does not properly squeeze the Config.Editor button into view from its right-alignment setting. And even after getting over those hurdles, in what is not working the Files&Attachment options that we coerced to appear are very different with regards to the different file type suffixes appropriate to word Documents. This I discovered by forwarding the failing email with the .docx attachments to my laptop which is running Thunderbird at version 150 where clicking on said attachments behaved properly. So, again, thank you so much for a timely and helpful assistance and for any others hitting a similar symptom I think the message may be that the fix is likely version dependent.