How do you make the chats list collapse?

Question

Hello,

Here is a picture of my current Teams app at work. Previously, the left chat window would collapse and then expand when I wanted it to. Today I noticed it is now fixed. How do I go back to making it collapse? Is this not possible anymore? I use teams in conjunction with outlook on the same screen. about 1/3 of my screen is occupied by teams. With it not being able to collapse now, I can barely see my actual chats on the right half of this screenshot.

This must have recently changes, because I could collapse this before.

Is there a fix for this? Thanks in advance.