Hi, I found not a lot of done tasks. Get there deleted autmoatically after a while?
No, tasks that were completed do not get removed at all, unless you do it yourself. We will consider adding such option in the future if requested enough.
how can I see task list that already done?
In the web, you can just go to a project and click on the "Show completed tasks" icon (clock) in the lower right corner to view previously completed tasks.