Hello,
Someone found a fix on StackExchange :
https://emacs.stackexchange.com/questions/48553/indentation-broken-with-all-inputfiles-tex

Le mer. 27 mars 2019 à 13:27, Glenn Morris <rgm@gnu.org> a écrit :

> Thomas Bucaioni wrote:
>
> > When pressing the TAB key, the indentation doesn't happen. Even, the
> > text is translated as in a Word or LibreOffice document.
>
> Please give a minimal complete example starting from emacs -Q.
>
> > In GNU Emacs 24.5.1 (i686-pc-linux-gnu, GTK+ Version 3.22.11)
>
> Please try the current release (26.1 at time of writing).
>