Just had two moments in this April 2020 where found two users with more than one answer to one particular question. Once i've done that in Game Development Stack Exchange (two answers with two different takes) and one of the moderators merged both answers and deleted one of them, so I assumed this was the right procedure overall.
Therefore, my take once saw the multiple answers from the same user was to flag them with moderator attention with a message similar to...
This user has more than one answer to this question which could be merged.
This morning was doing Late Answers Reviews and while flagging one noticed a message saying some of my latest flags weren't accepted. They were the two cases where the users had.
In of of the times, the moderator says
As long as they are using different approaches, it should be fine.
In the other, the moderator says
a moderator reviewed your flag, but found no evidence to support it
So, to answer your question, this might be something moderators deal differently depending on the community. While in Game Development Stack Exchange that isn't accepted and the moderator acted upon it directly, in Stack Exchange it's clearly accepted.