Additional chat-related features and issues within Microsoft Teams for business
I've tried this but then I'm bombarded with popups for new teams and then after a while it upgrades automatically. This may be due to my company's policy but trying to stay on the old version hasn't really worked for me.
If you resize the window slightly the scrollbar will appear. It will disappear soon after but if you can grab it before it does so you are able to use it.