Usually, when a user account cannot be removed from a Chromebook, it can be a couple of things which I will explain.
1. If the Chromebook is not enrolled in our management sometimes you will not get the option to remove user but instead have to powerwash/OS re-install instead.
2. If the Chromebook is enrolled in our management system but the "remove this user" is not visible to click on, then you will need to use the keyboard keys only to navigate to the "remove this user" options. This was first seen around ChromeOS version 70.
From the sign on screen where it shows all the user accounts, navigate by using the keyboard only
- hit tab until the little down arrow next to the user account you would like to remove is selected
- hit enter to select this little down arrow
- Now the "Remove this user" option is selected (if not you may need to hit tab again to select this option)
- hit enter again
- Then the second popup window will explain that "all files and local data will be erased....." and you may not be able to see the second "remove this user" option which is located at the bottom of this popup window
- hit tab again if needed or if you already see the blue selection box located where the second "remove this user" should be toward the bottom of the pop-up window then hit enter
See the video for the steps above