I really do empathize here, after having to use Teams for around 2 years. It's amazingly slow, confusing, buggy (it would crash the tab quite regularly), and just generally a perfect role model for what software shouldn't be[0].
I'm still quite amazed that Microsoft decided this was acceptable. I'm curious how Slack performs; perhaps they're not trying harder because there's no[t much] competition in this space ...?
[0]: (If I remember correctly, they were using AngularJS at the time, but I'm sure they're now using the regular React stack.)