Thank you very much for trying to help me out, Daniel!
I've tried this as well as many other solutions. But to no avail.
On my mobile, I can switch between my work account and my private account without any problem.
When I choose for my private account, I get the question: do you want your personal account or your business account (in my case: my former school). When I select 'personal' I get to my own private, personal MS Teams environment.
So the conclusion is: on my mobile it works as intended, but on my desktop there is no way of reaching my own personal MS environment.
Even when I log into Windows 10 with a local account, and I try to login to MS Teams with a unique alias to my private account that is different from my school account (and work account).
Also, when I am logged into my work-OneDrive account on my personal desktop it starts uploading private documents (desktop, download folder, etc.) to my work tenant and there is no way of stopping this. I uninstalled OneDrive from my desktop, and it messed
up some kind of symbolic links to my desktop now leading to a 'broken' desktop folder that cannot be used anymore.
In other words: working with multiple MS accounts (private, work and school) on a desktop is a total mess at this moment.
I sure hope Microsoft will fix this soon because this really is the biggest hurdle for the entire MS365 adoption imo.
(Btw, my job atm is doing the MS365 adoption for a large hospital with 19k accounts.)
Kind Regards,