The Attach button was moved in version 60. Maybe the What's New document will help you find it. https://blog.mozilla.org/thunderbird/2018/08/whats-new-in-thunderbird-60/ Attach and Insert are two completely different items so if you want to Attach you would not be looking for the Insert command that is found in the menu system.

There is no attachment button !, the link you sent did not help. When I compose a new mail I don't see any attachment button, pressing alt M only starts another mail composition.

What version are you using? Post a screenshot of your Composition window so we can see what you are seeing. Maybe someone else will have a suggestion for you.

+Finally found the button in the extreme right corner of the screen, sorry, a bit stupid of me. But why in the extreme corner and not next to the other buttons where I expected it ? Thanks anyway !

So it is right where it shows in the picture I linked to? I am surprised that link was not helpful.

I have heard that you can move it like other buttons on the toolbars. https://support.mozilla.org/en-US/kb/how-customize-toolbars Version 60 is too buggy for me to install so I will leave that to you to try.

thanx