Help with unlinking Microsoft Account from Windows 10 local admin

My issue is as follows :

I made a custom windows service in C#, and in order to install it, I have to input a username and password. However, it's not taking in any of the infos (I reset the password 3 times and each time it failed, I tried with both the username and the email address for both, I also tried the microsoft NIP in the off-chance that it would work). So, fuck microsoft and their account, I want to just unlink my PC from that account entirely.

Sounds easy, and from microsoft's customer support, it should be; just click the remove button.

Which doesn't exist. I AM logged in as administrator, I am 100% certain of it (this is literally the only account on the computer, it's impossible for it to not be the admin account), but the remove button is simply not there.

Alright, I should just log in locally then, right? Should be easy.

Except again, because microsoft, it isn't. I try to log in locally, put in my NIP to confirm it is indeed me, and then I input the username I want to log in as, the correct password... And it's telling me that there's already a user with that username. Yeah, no shit there's already a user, I'm trying to LOG IN AS THAT USER.

So basically, I'm entirely stuck here. I can't log in locally, I can't remove the link to the microsoft account and I can't install the windows service, which means I cannot run any of my tests. And, as usual, microsoft's customer support is basically as useful as curling my hand into a fist and shoving it up my own ass. Any help regarding this is greatly appreciated, since I effectively can't work until I figure out how to work around microsoft's "securities".