I haven't read the whole thread tbh, but my understanding is that Outlook mail flags mails as spam on the server side. So most settings just don't do anything at all. I have everything Apple and use the native mail apps, my mom uses the outlook apps. We have the same issue, so it doesn't even matter which app you're using because it's outlooks servers that makes the decision whether it's spam or not even before. the mail client receives it..
The most important mails go into junk but sometimes fishing gets through as if it's real somehow. This has been going on for years, with usually some small periodes where a large number of emails from addresses which normally are delivered just fine suddenly get send to junk, but last weeks I've had many important mails go to junk right away. A bill from my dentist, 2 mails about a submission to a hospital to name a few. I am lucky I can set up that I still receive notifications from the spam box on my iPhone but I still keep missing important emails.
This is getting insane, Microsoft. I've been using 'Hotmail' for years but I'm almost being forced to migrate everything to another mail server.