Is that how it is these days? If I log with my Microsoft account on a Windows device, the username used is only part of my first name. It always annoyed be that it was cut in a very unnatural way and I had no way to change it. I searched for some way to fix it and what I found said it was auto generated way back in the first time I used it on a windows pc and that it was saved in my account in some attribute that nothing ever updates.