Can't get MS teams to work

I have a MacBook Air and I-Mac using OS BigSur 11.3. and now have the need to use MS teams on a regular basis. I have tried to download the Mac version from Microsoft website, all downloads fine and then I just get a screen saying "Teams is loading........." this just stays and never actually loads. I have a Office365 account through my institution and can access all the other MS applications, just not teams. If I try to access Teams through Office365 I get this screen. Every time I press "I'm back" the same screen just re-loads. Does the same on both matchbook air and I-mac so I don't think it is a device problem. I have tried un-installing and re-installing several times.

Is there a simple fix for this?