Hey, I have the same problem as you. The auto login in MSFS2020 is the wrong account that I do not have access to anymore. No way for me to pass the sign in page. Just bought MSFS, so its basically a rock. I saw that you used a different computer. What exactly did you do? Did you install msfs on a different computer and log in? There is absolutely no help on this topic.
Things I’ve tried. Logged out of and logged back into microsoft store, xbox app, verified my PC was using the same account. Uninstalled MSFS multiple times, deleted some xbox credential file. There is nothing else for me to do. I dont even know who to contact about this. I bought this game on steam.