I believe that what you are looking for has now been merged with the Stories tab. There, you can go to Sprint status to see the state of the current sprint. Other functionalities that used to be found there have been deprecated.
Let me share with you a trick that you can view what you wanted to view from Planning Tab,
first open Stories from collaboration and click on more
then click on Switch to old UI
then once you get switch, re click on switch to new UI
and here you go, all tabs are available to use. I don’t know what is making this trick works but it will be removed by 31/AUG. Have fun!
Ah, i was lost for this as well, i had a feeling it was an outdated UI option. Thanks for the explanation!