Hey @Dang1, Michael from Asana here.
The reason why Tasks appear in your “My Tasks” is because those Tasks have been assigned to you. If your Project has been deemed completed by your Team & archived, regardless of Tasks being marked completed, your incomplete Tasks will still show up in your “My Tasks” as a default.
I want to echo what @Diakoptis noted about un-assigning those Tasks from yourself as the best way to remove these Tasks from appearing. Both @Diakoptis & @Caisha also provided great hacks for hiding these Tasks within collapsable categories above, which are useful in case you need to return to these Tasks later (if they are personal Templates, for example) but don’t want to lose track of them by un-assigning them from yourself.
When Projects are archived, they are meant to be removed as options from prompts where they would otherwise be auto-populated. When files are archived “in real life”, you want them to be able to be found at some time in the future when they’re needed, but not necessarily be in spaces where they can clutter your present work. The same logic holds true with archived projects in Asana.
That said, I think your suggestion to remove the assignee from incomplete Tasks in Projects that are archived is definitely worth suggesting in our Product Feedback section.