I came across What is the command to switch to normal user? and was a bit mystified that the question is closed as a duplicate of a largely unrelated question.
The closed question asks how to switch to a regular user after you have successfully obtained privileged access with su or sudo.
The current duplicate su command + authentication failure asks about authentication failures, probably because the OP was trying to input their own password to su (this is correct for sudo, but wrong for su). There are answers which (tangentially) explain how to switch to a regular user account with sudo su; but this is at best an obscure answer to a slightly different question, and arguably not a good answer to the question about authentication failures.
I have not spent a lot of effort on searching for additional duplicates; it is possible that there is a better duplicate and that the duplicate target should simply be redirected.
(The reason I want it to be reopened is that it lacks an answer specific to sudo which I was looking for, and found an answer to on a different site. I'd like to be able to add that answer to this question, too.)
walter@walter-VirtualBoxnotroot@walter-VirtualBoxso I don't think it is about switching back to a normal user. My first guess is that the OP is used to working as root, so they want to switch "back" to root which is their "regular" user.