Hi, I am creating a PoC application in which an user has to approve multipl

The point answer to your question is - yes, with Task plugin, you can pick up the tasks the user has access to and view the data as a task itself and the user can do an approve all and you can have messaging to address the issue.
A better solution is to use 'in-line approval' of tasks in Appian. Although this is not a 'select all', this drastically reduces the effort on approving a task by simply swiping the screen on the mobile device or clicking the 'Approve' link next to the task in a Tempo interface. I would strongly recommend the latter as a more scalable and better architectural decision.