Frankly this, as a developer. I call them "showstoppers" and if there is a god of programming, they are the ultimate sin. Things like
- breaking a user's multiboot
- deleting user data
Even if these are not bugs and merely the result of bad UX (lack of warnings and security for the user).
Deletion of all user data upon upgrade was a common 'problem' with earlier versions of Windows (I remember having such problems into the XP era, and I hear it happened to people on W10). Breaking other installs by MS is a common theme too in dual boot setups (whereas Linux bootloaders are more likely to pick up the Win install and offer access to it).
I remember vividly the last time it happened to me. I had been dual-booting Linux for some time (on a personal laptop dedicated to work). It was my first Linux OS, I was a newbie (precisely learning bash, programming for servers, etc). After some update, Win10 broke my dual boot. I was livid. It took me the better part of a weekend to fix it and avoid loosing all my work of several months (a lot of it was in the form of system files all over the place, I had no idea how to retrieve all that without ad hoc commands etc, and I had no idea what e.g. chroot was at the time. I learned, the hard way, haha — btw thx to the Arch Wiki for that weekend. It was a life saver).
The very next thing when I got access back to my Linux OS was to backup all my data, format everything and reinstall Linux fresh.
And that was it.
I've never used Windows ever since as my primary driver, only for testing purposes in VMs. That was 2016 iirc.
There are such things as showstoppers that make you instantly drop a product, never to look back. Microsoft's Windows desktop team never learned that, I don't know how they still pretend to be for "professionals". You don't do that to people who make a living with their computer (i.e. the vast majority of businesses nowadays).