The objectif is to have a "to do list" by ticket (each ticket has her "to do list") with the possiblitie to add a new item in the to do list directly from a ticket. ?

This looks like Cehcklist.
Or just Actions linked to the ticket.

Other solution, have the possiblity to add new task directly from ticket (Task Tag)..

It's easy adding a link to activity and creating it in one step, or copy ticket as activity.

Hi Babynus and thank you for your quick answer..
However your answers are not optimize (it's my opinion ;-)). In fact relative to your answer and if my understanding us correct, i have to go to in action menu to create an action and after, create a link in the ticket... We have a lot of manipulations to do .
My proposition was : create directly from Task Tag in the ticket, a new task. (see attached file)

Thank you for your futur reply

In fact relative to your answer and if my understanding us correct, i have to go to in action menu to create an action and after, create a link in the ticket... We have a lot of manipulations to do .

In fact it' not as complicated as you can directly create the action while adding the link.
Click + to add the link, select action, click magnifying glass, then +. you create the action and will go back directly with link created.
Bjut maybe it's not as simple as you wished.

My proposition was : create directly from Task Tag in the ticket, a new task. (see attached file)

Unfortunately, job list is not designed this way, it is designed to propose a fixed list. But maybe the concept could be improved. Ticket #4655 recorded.

I'll follow this evolution with attention 😉