Lots of things are bad about teams. Here's one that annoyed me the other day: In a channel, I opened a power point presentation. It opened within Teams. I wanted to message someone about one slide. To do that, I had to leave the presentation, navigate to the chat section and search for the person I wanted to message. When typing out the message I realised I wanted to copy paste a phrase from the slide... but now the presentation is closed. So I go back to the channel, open the presentation, go to the slide, copy paste and then close the presentation and go back to the chat - infuriating!

tldr: everything opening within teams is a poor ux