I have had this happened to me twice. I installed the current Odin release and set it up (installed some apps, changed some settings). I also rebooted several times, for example after installing the nvidia-470 drivers.
At some point i noticed the rather convoluted hostname and decided to change it with:
sudo hostnamectl set-hostname newhostname
After that I rebooted and was thrown in the second part of the installer where you need to (again) set your keyboard layout and the create your user account.
When I entered my existing account, it said, this account is available (it showed a green checkmark) but when I proceeded to create that user, it complained about the user account already existing.
I created a new account and looked around in the system. The home folder of my old account is there, but I can't login with that account. It only shows me the new account.
Interestingly, the account page in settings only shows my current account (jonathan), but when I click on
Unlock to change some settings, it shows my old account (inhji) as a choice:
Also, if I try to create a new user with the old account name, the user creation window just disappears after clicking on "create user".
Has anyone had this happen to them before?