I want to hightlight Tasks tab when user logs in. This is to show tasks to the u

This is currently not configurable but can be easily "achieved" through a "non-invasive approach" by providing a direct link like the one below (replace with your actual URL) to your end-users so they always go to the Tasks view rather than the News feed:

http(s)://xxxxxxxxx/suite/tempo/tasks/

Depending on the web server you could also force a redirect from URL ENDING in /tempo/ to /tempo/tasks/ but you want to be really careful and make sure the rewrite rule is accurate enough to redirect users when the URL is exactly ENDING with /suite/tempo otherwise you could be impacting the functionality. That said I wouldn't recommend doing this if you are not familiar with the web server rewrite rules syntax.