Self hosting my emails, grade of 100/100 on mail-tester, I'm on none of the dozens of blacklists I've queried... and Microsoft marks every single one of my emails as spam.
Just because you're lucky doesn't mean other people are "unexperienced". I don't know what experience has to do with it tbh. Maybe if you have experience working for Microsoft and you can contact the right people there...
Have you contacted Sender Support at Microsoft? They're very responsive and if your mail activity is legit they'll certainly help you solve the issue. Also make sure you set up the SNDS dashboard so you can view your IP reputation: https://sendersupport.olc.protection.outlook.com/snds/index....
In my experience the difference in outcomes that people have with self-hosting mail are largely down to, from most important to least, (1) the nature of the mail they are sending, (2) their choice of hosting provider, and (3) the correctness of their mail server setup. It sounds like you've got (3) sorted, so maybe (1) or (2) are relevant here.
Just because you're lucky doesn't mean other people are "unexperienced". I don't know what experience has to do with it tbh. Maybe if you have experience working for Microsoft and you can contact the right people there...