You need Thunderbird version 128.4.0 or newer.

Thanks for the information but it's impossible to upgrade fro 115.9.0 to 128.4.0 Why ? It's a mistery !

Help > About fails to update?

??? I don't understand....

It's so strange that Mozilla annonces a new application but impossible to install !!!

You are using Windows 10? Do Help > About. Make a screen shot

Post the screen shot here with the Browse button of "Add images", below the comment box.

I'm using Windows 11 (64). I dont'see what to show you with a screen shot. The problem is that I don't see any proposition or option to upgrade My version of Thunderbird is now SUPERNOVA 115.9.0

Post the screen shot please.

I've posted the screenshot

I've posted the screenshot

Thanks - that is what we needed. I see now that a) it is 115.9.0 which is not even the latest version of 115, b) the installer is msix.

Did you get this from the Microsoft Store?

I'm using Thunderbird since so manmy years (20?) that I don't know. When there's an update I Install it, When I change laptop I reinstall it, but my Dell computer is already 5 years old so I don't remember...

...well, I'm leaving for travelling tomorrow and wanted ti have Thunderbird app running on my smartphone but it seems a bit complicated. Childhood illness ???

Check the Microsoft Store and (re)install from there.

Thunderbird desktop ?

It's complicated to reinstall. Don't have time now. Things should be more simple for old clients and iusers. What a mess...Wea re not all geeks !

hope you have a better solution when I come back in 10 days. Thanks. Best regards

As best I can tell you would have originally gotten it from the store, unless someone else installed it for you. Anyway, it was installed using the msix file, and that is what the store gives you https://apps.microsoft.com/detail/9pm5vm1s3vmq?hl=en-us&gl=US