Browser compatibility and teams in incognito mode in Chrome

I also see all of those problems regularly, >1 year after your post.
Teams browser compatibility can indeed be described as "only recent desktop Chromium".

In the past, more browsers worked, after setting "user-agent" to something supported and going into "desktop mode" if applicable.
Microsoft EdgeHTML (the original Edge, not the version that surrendered and became Chromium on the inside!) of course worked (and was even promoted by Teams!). But MS dropped the (real) Edge browser entirely in 2021 and made its installation difficult.

Now, Mozilla (Firefox) & Apple (Safari) are the last major web browsers that are not Chromium based.    Safari is WebKit, which shares most of Chromium's engine other than JS, so really the world has only 2.5 web browsers.

One could argue that MS Teams isn't imposing the lack of diversity but rather is embracing the monopoly in order to simplify development.
But even that doesn't account for the poor compatibility.
Mobile Chromium (the most popular web browser in the world!) was usable until only days ago,  albeit with some glitches related to auto-pan/zoom.
And circa-2019 Chromium was usable until a few months ago.

So, Teams compatibility has undeniably been worsening.
If the Teams app was efficient, this might be understandable as the web being a secondary client, like in WhatsApp.
But the Teams app is Electron, meaning you're forced to run an additional copy of Chromium, without the latest security patches, and with unknown new problems introduced.

Teams also has no practical 3rd-party clients, and probably doesn't document enough of the API to enable them.

It's hard to avoid the conclusion that Teams is actually intended to force a Microsoft pseudo-platform onto all the world's primary information terminals, via a backdoor that Facebook and others pioneered.     I.e.  Teams is meant to achieve what Windows somewhat-unexpectedly failed to do.   The Electron app is an opaque monolith, demanding vast permissions.  It grabs a whopping 700MB of cache on my mobile devices, within minutes of installation, even though I haven't accessed any content beyond text and small images.   And so does the Teams website!

Teams more befits the Microsoft of the 1990s-2000s than of today;
In the last 10 years, Microsoft has been steadily embracing open source and non-Windows platforms.
MS Azure is majority Linux.
WSL(the Windows Subsystem for Linux) generally works well.
Microsoft .NET led the way by becoming truly free, portable, and lighter weight than the classic version.   (How ironic that the Java world went the opposite way on all 3 points!)

Teams is an aberration that hasn't yet gotten the pushback that it deserves from both technical and social considerations.
Microsoft _is_ quite receptive to customer concerns (unlike, say, Apple), so Teams users, please speak up!