Today?
Where were you when it's 'free' OS' was 'phoning home' or during it's behemoth days in the 90s-2000s when it forced the most pro-business Government (US) to essentially break it up when it was using it's monoploitic practices too far for even them?
I have to use Teams and just logically assume all of what was said or talked about exists on some server somewhere for the employer, LEO or intelengence agencies to retrieve; if Snowden has taught us anything is that M$ is the darling child of the Intelligence agencies in the US for a reason.
Using M$ outside of a (forced) work environment is literately like asking to be tracked, monitored of your own accord. Nothing they do should be presumed to be secure until proven a length to be otherwise. It's very likely why it's so bloated and runs terribly, they are optimizing no for UX but for it's real business model: spying.
Sadly, and with only a slight tinge of despondence: I've given up on preaching about FOSS to the masses, but with stuff like this it's like asking why people sign up for death cults, it alwasy ends in: Humans just being Humans.