I do have to use Teams occasionally for work and bizarrely the web client in Firefox works far better than the native Linux Teams client. Not particularly difficult as the Linux Teams client wouldn't do anything except display a blank box (this was on Ubuntu).
The European Economic Area + UK also have a lot of telecoms and networking experience. If they have to pay for improvements to edge networking for a reliable replacement for Teams they could easily bring farm that work out to their telcos.
With enough political motivation barriers will be removed one way or another.
I hadn't heard about PWAs (Progressive Web Apps) before, but it doesn't look like they're commonly used on Linux. At a first glance, they look a bit similar to ActiveX to me.