Viewing planner in Teams will not allow you to attach a file - the attachment button is missing
I have one of my planners attached to a Teams site as a tab, when viewing the planner, it will allow me to create tasks but will not allow me to add an attachment to the task as the attachment button is missing.
If I open the item directly in Planner I can attach files!
This is similar to the other issue I found where if you view any of your tasks via "my Tasks" within planner then it will also not allow the attachment of files.
This is also an issue for me, it leads to inconsistency and the need to open up the browser to work on it.