What freaking organisation is always my response; I've never been able to figure it out.
Very random example: SharePoint has a MS Word integration - you can open a .docx file from there, it opens in Word and you are actually able to edit the file on the server as if it was on your computer. At least in the older on-prem versions, this actually used the Word installed on your computer, not some web version. If you used a custom authentication provider, a little browser opened within Word and you had to log in there. But Word needed to "trust" the domain. On a personal computer, you could just edit the trust settings in some Word menu, yet the error message still said "your organization..." if you didn't.
Additionally, go to Accounts in Settings and double-check that you're not logged into any "work or school" accounts.
The one thing I can't stand is that if you log into a non-personal Microsoft account in an app, there's a dialog that is very confusing[1]. It asks if you want to use that account everywhere on your device, but there's a box checked by default to let the organization manage your device, a button that says "Yes", and what looks like a hyperlink that says "This app only". I always uncheck the box before clicking "This app only", but I wonder if keeping that box checked would still enable organizational device administration. It screams "dark pattern" to me.
1: https://i.stack.imgur.com/gmp00.png
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Just to add a tip for others: If you want to use Edge for the Windows optimizations and PlayReady support for streaming services, but don't want to deal with all the annoyances, you can disable many of them via Group Policy[2]. For example, you can disable the "Search Bing in sidebar" option that shows up in context menus[3] that I always seem to accidentally click when I'm trying to search for something I highlighted. I also use Group Policy to set the default search and homescreen settings because then it won't annoy you with the recommendation to set it to Microsoft defaults every time it updates.
Firefox is my main browser, but I use Edge for streaming Netflix and the like because I don't get 4K playback via Widevine. It annoys me because Edge would actually be a great browser if the Bing folks weren't constantly trying to shove things down my throat and filling it with dark patterns.
2: https://learn.microsoft.com/en-us/deployedge/microsoft-edge-...
3: https://learn.microsoft.com/en-us/deployedge/microsoft-edge-...
Windows is full of dark patterns, so I don't really know why I had even a modicum of doubt.
Between the aforementioned dark pattern with the buttons/not-buttons (they didn't even bother to vertically align "This app only" and the button), the not-a-question "do what we tell you" phrasing, the blank title, and a dialog that's overall around twice as tall as it needs to be, it seems recent Windows is unfortunately full of user-hostile and also disgustingly amateurish WTFs like this.