I use Wayland at work, and haven’t had any issues sharing my screen on Teams.

I have a Linux work laptop which they let us have but we still have to use the MS crap. Fortunately most of it is accessible through the browser but a lot of the Office apps are broken, or missing features on web.

Why their devs choose to upgrade toolkits this way I cannot say.

I forget the exact details but iirc Evince was a special case because rendering PDFs in GTK4 was so different that they essentially just had to rewrite the whole application. I think Gnome Papers still doesn’t support the full feature set that Evince supported (although it works well for most use cases now). This is why its still not the default for Gnome, although I think Ubuntu has decided to adopt it a little early.