Trouble after renaming home folder

I bought a new Mac and transferred the home folder of my old Mac. There was a home folder on it already, but I choose not to overwrite it. After renaming my home folder, using these instructions: Change the name of your macOS user account and home folder - Apple Support things went wrong.

Now an empty folder with the old name keeps popping up. So now I have an extra homefolder. When starting up I choose the [newname] account, but instead I get the empty [oldname]account, even though it is not visible in Users & Groups. But the [oldname] homefolder is in my navigation bar in the finder. Deleting the home folder with a second admin account has no effect. After restart I am not in my [newname] account but in my [oldname] account, with all the hassle of re-registering and logging in on my AppleID. The [newname] account is still there and I can see the files (that shouldn't be possible, I think).

I guess wiping the new Mac and starting all over would be the easiest way, but is there a faster way to get rid of this pesky folder? Any advice is appreciated.

From 2013 MBP 15" to 2023 M3 MBP 16" macOS 14.1